Yes, it's Princess, not Queen, and makes more sense this way. While the Queen's whereabouts may be unknown, Princess Marle actually, literally, vanished. Sorry if I confused anyone by having it wrong for as long as I did. In my defense, 王女 resembles both 女王 and 王妃, which both mean roughly "queen". More recently, I amended "The Vanished Princess" to "The Princess who Vanished" to parallel the previous chapter ("The Queen who Returned").

The music doesn't start again until Crono heads downstairs. Someone calls out as he reaches the ground floor.

Lucca runs up, clearly out of breath.

I wonder how she got past the guards...

Lucca: *pant, pant*... looks like you're safe!
More importantly, what about that girl?

Lucca: Huff, puff...you're okay!
Did you find the girl?

Lucca: GONE?!
Whadd'ya mean she's gone?!

Lucca: When she disappeared, I could
have sworn I'd seen her before.

Lucca: This IS our kingdom, but it looks
like the kingdom from quite long ago.

Lucca: And this looks identical to
the castle in OUR time!

Lucca: That means she was
mistaken for her own ancestor.
That girl's nobility even in our era...

Lucca: I'll bet they mistook
that girl for her ancestor...
You see, she's a member of the royal
family in OUR time!

This is why the pronounciation of her name matters a bit. The full name given here is exactly the same, but with 'dia' added (and that's pronounced 'dee uh', not 'dye uh'), making the full thing sound roughly like 'marldia' because of the weak vowel. Not only that, even if you named her something different, the game will actually take the first three characters of that (or the whole thing if shorter) and tack 'dia' onto it, so it works out regardless, though you could get some rather odd names. The NA version always makes her name "Nadia" no matter what the player picks, and even the default name "Marle" only vaguely resembles it. The JP version makes it impossible for both versions to be identical (the long name is too long), but the NA version allows selecting "Nadia" as her short name.

Crono looks shocked at the news. It explains a lot, though. And Lucca's not finished explaining yet...

Lucca: Marle, that is, Princess Marledia,
is a descendant of this era's queen.
This era's queen was kidnapped...
The way it was supposed to end up
after that is that someone saved her.
But we've changed history...
In other words, since Marle appeared in
this era and was mistaken for the queen,
the search for the real queen was called off.
If the queen were to be killed...
Marle's existence would vanish...
But we're still in time!
If we can help out the queen even now,
history should go back the way it was!!

Lucca: Marle, that is, Princess Nadia,
is a decendant of Queen Leene!
Queen Leene has been kidnapped.
As I recall, someone was supposed to
have saved her.
But history has been changed!
Marle looks so much like Leene,
that they probably called off their
search when she appeared here.
But if the real Queen is killed...
... Marle will simply disappear.
There might still be time!
If we can save Leene, history as we
know it should remain unchanged!

Lucca: In all likelihood, something's
happened to this era's queen.
That's why the very existence of
that girl, her descendant...

Lucca: Something must have
happened to the Queen in this era.
As a result, Princess Nadia
ceases to exists!

Lucca: In any case, we've got to search
for the true queen's whereabouts!

Lucca: Hurry!
We have to find the real Queen!

The internal storyline progression tracking variable is now 0x12.

Toma's remarks in the pub point to the abbey to the west, but his clue isn't the only one. For one thing, the chancellor is acting suspicious...

Chancellor: How did she get back here?
It shouldn't have been possible for her
to make it out of there on her own...

CHANCELLOR: She escaped?!
But how?
She was in a secured room!

Some of the knights have noticed unusual behavior too, though that's not all they're talking about.

Not everyone agrees about the chancellor, though.

On the other hand, Toma did call the abbey suspicious, and the events in its history seem a bit too convenient to take at face value...

So Crono and Lucca decide to take a look at this abbey to the west.

At first glance, it looks just like an ordinary small chapel, with ordinary nuns. The holy-sounding, for lack of better words, 1-15 マノリア修道院 (Manoria Abbey) plays. And then Crono spots something on the floor.

Lucca: Did you find something?
A headdress...?
This's the Guardia royal
family's coat of arms!

The nuns surround Lucca and Crono. Shedding their disguises and attacking, each is revealed to be a Mianne (Naga-ette), a half-snake monster.

Lucca fights with a gun, but pulls out a hammer to hit with when at close range. Her stats are very similar to Marle's, with the differences being Lucca's somewhat higher hit points, hit rate, magic, magic points, and stamina, but lower speed and slightly lower magic defense and evasion. With tech points, she learns two techniques (one of which combos with Crono), then stops learning more, just like Crono and Marle. Her status screen has a red 火 (Fire) in the top corner, and much as Crono and Marle do for their respective elements, she has a 20% innate resistance to Fire-based attacks.

Another one suddenly appears and takes a swing at Lucca. 1-23 危機一髪 (Critical Moment) plays, but only very breifly, since right after Lucca screams...

...a froggish humanoid creature drops in and smites the foul demon with his broadsword. 1-20 ファンファーレ１ (Fanfare 1) plays. The newcomer wears simple armor, blue gloves and boots, and a forest green cape. He's also green and hops, and typically makes a ribbit noise when he speaks.

: Never let your guard down before the end.
It's when you're drunk with victory
that your defense is wide open.

: Did you also come to aid the Queen?
It looks like their lair is in here.
So, why don't we go in together?

Allow me to express my disdain for the NA version rendition of the frog's speech. There's no reason to have him use Elizabethan English, since he speaks normally (a bit coarsely, even) in the JP version—though his speech does tend toward a more ceremonial tone in certain special situations, such as when speaking to the king, it's not how he typically talks—and it's a horribly mangled mockery of real Elizabethan English most of the time anyway. For example, "Will thee accompany me?" should be "Wilt thou accompany me?" if he's speaking to only one of them, and I believe it should be "Will you accompany me?" or "Will ye accompany me?" if he's speaking to both. "Thou" is a subject, "thee" is a direct object, "thy" and "thine" are possesive, and all of them are singular. It's too much work to point out all the problems, but I'll mention some of the ones that particularly bug me...

Though I suppose you could always argue that poorly-phrased outdated language is a side effect of his curse...

Lucca: Y-you're...!?
Crono, you know, right?
I can't stand frogs...!

: Well, given how I look I guess there's
no point in telling you to trust me...
Fine, do as you wish.
But I've got to help the Queen out...

Lucca: H-hold on...
You don't seem like a bad
fro... person...
Umm...
What should we do, Crono?

Crono decides to work with the frog person. After all, he's skilled, familiar with the time period, and has the same goal.

Or else Crono gets stuck in another "But Thou Must" dialog loop until giving in. I'll stop mentioning these from now on.

Lucca: L... let's put up with it,
and go together!
What's your name?

Naming time again. And the default happens to be...

Lucca: Yes, well then...
Don't be too hard on me, Frog.

Frog: No problem. I'm positive there's a
secret passage somewhere in this room.
I'll bet we can get in the back from there.

The internal storyline progression tracking variable is now 0x15.

There's a conspicuous organ in the corner. Crono plays around with it, resulting in 1-16 道行く者へ祈りを… (Prayer to One Who Walks the Road...) and a secret door opening in the rear wall. In the secret section, 1-17 沈黙の光 (Silent Light) plays. Of course, there are monsters all over.

In addition to more Mianne, monsters here include Diablos, Biter (Gnasher), Servant of the Magus (Hench), and Mad Bat. Many have low magic defense, and several have a specific weakness to fire, so Lucca's Flamethrower and her Blaze Wheel combo with Crono work particularly well, especially when the monsters are nice enough to group together.

Besides using a broadsword, Frog has techniques of his own, and can combo with Crono on one of them. Like the others, he stops learning skills after his second. His status screen has a blue 水 (Water) in the top corner, like Marle's, and he similarly has a 20% innate resistance to water. His stats are similar to Crono's, though he's not quite as fast, and his HP, power, and stamina also lag a bit as their levels go up. However, he has a small edge in hit rate, evasion, and magic defense, and a larger edge in magic (which isn't to say his is high, just that Crono's is noticably worse).

Look around for the usual scattered treasures. There are also a few interesting rooms. One, behind a spike barrier that a nearby skull-like switch on the wall easily deactivates, holds two captive Guardia soldiers and a Power Capsule.

In another room, "Courage and Pride" plays, and amazingly enough, King Guardia, a soldier, and a woman in a queenly dress stand here. How suspicious.

But try to leave after speaking to the soldier or queen (oddly, the king doesn't count), and...

They turn into three Biters and attack. Shocking. The music stops after combat, and reverts to the area's usual after leaving.

Another room has several monsters at a table, apparently snacking and getting rather tipsy. The lighthearted tune 2-14 愉快なスペッキオ (Merry Specchio) plays in this room. The monsters are surprised to see the party, but not for the obvious reason.

Well, as long as they're oblivious, let's try making conversation.

After the party talks to all of them, the Diablos turns to leave.

It heads to the room where the fake king and queen were, and apparently disappears. But there is a suspicious alcove in one wall, and through it lies a small shrine with a large statue, presumably of the Magus, being worshipped by a group of the local monsters. The poignant 3-3 夜の底にて (At the Bottom of Night) plays.

Chorus: Ah, great Magus♪
Great Magus~♪
Our salvation♪
Great Magus~♪

CHORUS: Magus, oh Magus ♪
Our Hero, Magus ♪

Interestingly, the subject of the statue appears to be human, long-haired and wielding a large scythe.

Chests by the statue contain a Protector and a Speed Belt. Contacting the bottom Diablos after the chorus triggers a battle with all five monsters here.

Another room has a sillier bit. Aside from the obvious chests, one containing a Lady Suit, the drawers to the left also contain something unusual...

ブロマイド (name derived from bromide paper) generally refers to promotional photos of stars, sometimes suggestive, and similar to pin-up photos.

However, three Servants of the Magus burst in the door one after another.

The pin-up photo does not appear anywhere in the inventory. Finding it just sets a flag that allows for a trade later on.

In the next section, spikes block off a central room. Stairs lead downward on each side, but whichever staircase is used first collapses into an unclimbable ramp. A back hallway has a note on the wall near the middle:

However, a switch in one of the side rooms removes the spikes in the central room, and fighting off the monsters guarding it allows access to both an Iron Sword and another piano there that reveals a door next to the note, which now reads:

Notice: There is a way for only those
who have decided their hearts to go.

NOTE: Try hard enough and you will
find a way in.

Past the next hall and a save point, the party reaches a larger chamber, where "Critical Moment" plays...

: Are you prepared, Queen Leene?
It's time to say goodbye to this world.

They rush into the room to see the queen being confronted by... the kingdom's chancellor...?

Chancellor: Oh? You...!!
I'm impressed you snuck in this far.

Frog: Your majesty, please stand back!
We will take care of this one.

Frog: Majesty, stand back and
allow us the honor!

Chancellor: Gya ha ha...! Give it up!
I won't let a single one of you
leave here alive!

CHANCELLOR: Gyah, ha, ha...
It's useless to fight!
No one will leave here alive!

Chancellor: Hah! Worthless frog...!
I'll make a bloodbath of you all!

CHANCELLOR: Stupid frog! It's time you
jumped off this mortal coil!

Chancellor: Chancellor...
Change!

Right after yelling "change", he turns into a big yellow slimy monster. It's the first boss battle! Except for certain special ones, boss battles use 1-18 ボス・バトル１ (Boss Battle 1).

Yakra strikes back at the whole party when attacked, unless too close to the attacker. Try to avoid attacking with characters who aren't in his face. He also uses a powerful single-target needle attack periodically, but like many enemies, makes it obvious when he's getting ready to do so. Crono and Frog's X-Slash is the only combination attack currently available that gets a damage bonus, while Lucca's Flamethrower should handily outdamage her normal attack. Keep your health up, and it should be over shortly with little difficulty. Yakra has no particular resistances or vulnerabilities.

Of course, the party emerges victorious, otherwise it would be a very short game. "Fanfare 1" plays until the party returns to the castle.

Leene: I knew you would come for me.
Thank you, Frog...

Frog: The king is worried about you.
Let us return to the castle.
Thanks for your help, Crono, Lucca.

Leene: Thank you very much.
Please come to the castle along
with us as well.

Before leaving, the party checks the treasure chests in the back. Inside one of them, oddly enough, is the...

Real Chancellor: Phew, I'm saved!
That damned monster, shutting
me up in a place like that...!

REAL CHANCELLOR: Phew, thank you!
That monster stuffed me in there.

Real Chancellor: Oh, my lady queen!?
The real me is here, as you can see.
I am perfectly lively!

REAL CHANCELLOR: Oh!
Your Highness!
As you can see, I am undamaged!

Leene: Yes.
Then let us return to the castle.

Real Chancellor: W-wait for meee!
The real me's here, as you can see,
perfectly lively!!

REAL CHANCELLOR: W, wait!!
What about me?

This more frantic line doesn't have the same level of ostentatious formality that the other one does.

He rushes out after the others.

The internal storyline progression tracking variable is now 0x1B.

No music as the scene begins.

Chancellor: That damned Yakra.
Replacing me, kidnapping
lady Leene, and all that...
Our Guardia Kingdom must
build a courthouse and prison
to strictly judge that sort!

Right, because the monsters you're at war with really care about that sort of thing. *sigh*... bureaucrats...

Frog steps forward. 1-19 カエルのテーマ (Frog's Theme) plays.

Frog: Unable to protect lady Leene
to the end, I have lost all honor.

Quick lesson in classical English: The '-th' verb ending is only for third-person singular subjects, such as "he", "she", and "it". For example, "he looketh", "she cometh", "it falleth", and so on. "I hath" is simply wrong. Similarly, the '-lt' and '-st' endings are only for use with the second-person singular subject (thou). For example, "thou shalt", "thou hast", etc.

Frog ribbits and briefly bows, but quickly leaves the throne room without saying another word.

The internal storyline progression tracking variable is now 0x1C.

Crono tries speaking to the king.

Leene: I thank you very much
indeed for saving me.
If you had come any later, what
might have become of me...?
By the way, where is the girl whom
they say was mistaken for me?

Lucca: That's right!
I'd completely forgotten
about Princess Marledia!
Hey, Crono!
Where did lady Marledia vanish?
Maybe there...

Crono and Lucca rush up the tower to the queen's room. Sure enough, Marle reappears there, and in her normal clothes, even though she was wearing one of Leene's fancy dresses when she disappeared. 2-12 ファンファーレ２ (Fanfare 2) plays, followed by silence.

Marle: Crono!
I was so scared...
Knowing I'm in a cold place even
though I'm not conscious...
I wonder if dying feels like that?

Lucca: My lady Princess Marledia,
I see that you are in splendid condition...

Marle: You came for me too!
Marledia...?
Huh!?
Looks like my cover's blown...
Sorry, Crono.
I didn't mean to trick you.

"Crono and Marle ~Distant Promise~" begins playing.

Marle: I am Marledia.
My father is King Guardia XXXIII...
But I wanted to wander around and look
at the fair with a boy as much as any girl.
If you'd known I was a princess...
Crono, you wouldn't have seen the
festival with me, right?

Marle: See?
And I like being called "Marle"
better than "my lady princess"!

Marle: That's just like you, Crono!
We're friends!

さすが (sasuga) essentially refers to someone living up to their (high) reputation or to someone's (high) expectations.

Marle: The real Queen's back
in one piece as well, right?
Let's go home too, Crono!

The internal storyline progression tracking variable is now 0x21.

"Courage and Pride" resumes upon leaving. Back downstairs in the throne room...

The Japanese expression literally means "a pair of melons", but that brings something different to mind in English.

Marle: If you don't get along well
well with the King, I'll get mad...
no, I guess I can't, either.

When I first played the NA version, I thought she meant Crono and Lucca had better run along home, forgetting momentarily that the castle in this time isn't her home. Looking at the JP version, it looks like she's actually saying that the King and Queen need to get along with each other, which makes more sense. There's a probable pun too; 怒る (okoru) is to get mad, but 起こる (also okoru) is to happen. Since neither kanji is used, Marle could also be saying she can't happen if they don't get along.

The king and queen look at her oddly.

Marle: Never mind. Anyway, may
you live happily ever after!

(Talking to the Queen again)

(Talking to the King again)

As the party leaves, they find Frog standing outside the throne room. He turns as they enter. "Frog's Theme" plays.

Frog: The Queen was exposed to
danger because I was near...
I'm leaving the castle.

Frog: 'Twas a fault of mine, which
endangered the Queen.
I shall depart for good.

He spots Marle and walks up to her for a closer look.

Frog: I see, you do greatly resemble
my lady the Queen.

Frog: Indeed, your resemblance
to the Queen is uncanny.

Frog: Crono, your swordsmanship
shows considerable promise.

"thou hast potential", not "you hath"... yeesh.

Frog, sticking with his decision, quickly leaves the castle. The music fades out.

Lucca: ...
You're not so bad either, Frog.

And where did Frog go? A soldier at the broken Zenan Bridge has part of the answer.

Apparently he's not exactly well-liked, and this isn't the only soldier to have nasty things to say about him. It's no wonder he doesn't feel welcome at the castle.

So, with history more or less back the way it was and Marle safe, the party heads back to hills where they arrived.

The monsters are stronger now, most notably the Badmadillo (Poly) halfway through. It's tough for a normal monster at this point and has an unpleasant counterattack, but low magic defense means Lucca's fire works well, or Blaze Wheel to maximize damage per hit.

There's no portal visible here, but there is some sort of small pulsing dark blue sphere. "Fanfare 1", which tends to double as Lucca's theme, plays.

Lucca: W-well then, Marle...
Please observe.

Lucca pulls out a strange device that bears some resemblance to a key. The sphere responds by opening into a portal, like the earlier ones.

Marle: Eeek!
Lucca, that's AWESOME!

Lucca: O ho ho ho...!
E-excuse me...!

Marle: You can talk normally, too!
You're more amazing than I am!
I might be a princess, but I can't
do a thing.

Lucca has, up to this point, been using the very respectful form of Japanese that is appropriate for speaking to people like princesses. Marle's apparently sick of this, and tells her to talk like she would to just anyone.

Lucca: Then I'll take you up on that...
I named this distortion a "Gate"...
A Gate is something like a portal that
links the same place in different eras.
As far as appearing and disappearing
goes, the Gate itself is unstable.
Accordingly, I applied the principles
of the Telepod, and use this...
Gate Holder to stabilize the Gate.

ゲート is just "gate" written phonetically in katakana. 門 is the kanji that means gate, portal, etc..

Marle: But why did this Gate appear
all of a sudden when it did?

Lucca: The Telepod might have influenced
it, or there may be something else...

Marle: This's kinda complicated...
Anyhow, let's return to our era!

Lucca: Yeah, okay.
Let's go back, Crono!

The internal storyline progression tracking variable is now 0x24.

They step into the Gate, it closes, and they pass through to the other side.

The Gate opens, right where it was before, and the party steps out. The festival music plays, as usual.

Marle: Yaaay!
We finally made it back!
Hey, Crono, Lucca!
Come with me to the castle?
I owe you one!

Lucca: I'm sorry, Marle.
For making you go through all that.

Marle: Nah, it was thrilling
and lots of fun.
I made great friends, too!

Lucca: Crono, you see her off
to the castle.
Be a good escort for her.
I'll try investigating the cause of
the Gate's appearance.

Marle: Later, Lucca!
Well then, escort me to the
castle, Crono!

The internal storyline progression tracking variable is now 0x27, starting the next chapter.

It's probable that Frog would have saved Queen Leene regardless, particularly given that he was already snooping around the cathedral. He most likely did so unaided in the original timeline anyway, given that the soldiers generally distrust him and would be more likely to suspect him of kidnapping the queen than to aid him in rescuing her. Since he had been acting as the queen's guard, that distrust may even be what he means by his presence endangering Queen Leene, though it's also possible he just agrees with the sentiment that Cyrus, the former protector of the royal family, would never have let such a thing happen in the first place. As previously discussed, Marle's disappearance may have been caused by an outside force that wanted to make Crono and Lucca think they had fouled up the progression of events in order to provoke them into action, rather than by any momentous change to history.

But even if we assume that disrupting the search for Queen Leene had any meaningful impact to begin with, that impact has been reversed regardless. Crono and the others have forged ties with the royal family of the era and with Frog that will be important in their later adventures, but appear to have no historical significance of their own. It's unknown whether Frog left the castle in the unaltered timeline, but that, too, seems to have no relevance in the grand scheme of things. In short, the party's net impact on history has been negligible at most. Then again, that was the idea... at least for now.