Our episode begins with Finn entering the main room of the treehouse to find Challenger, Marguerite and Roxton preparing for a trip.

Challenger explains that they are going to a mountain cave, 'where every year for two days the sun reflects of brilliant mineral deposits on the hills side in such a way as to bring two separate plains of reality together.' Marguerite chimes in mentioning that last time they found, 'a quaint village run by a disgusting little tyrant that tried to hang Lord Roxton and her.'(reference to the Second Season Episode 'The Outlaw')

Finn finds it odd that they would wish to go back there, but agrees to tag along for the trip.

But first, Marguerite needs to go on a quick treasure hunt for some gems she's buried, once she has them safe in hand, off they go.

The group reaches the cave; they enter to find the bright light of the fissure just as it was the last time Marguerite and Roxton found it. Marguerite, Roxton, and Challenger approach the fissure, while Finn pulls back. A face begins to appear in the light of the fissure that Finn seems to recognize, she turns and runs from the cave, Marguerite, Roxton, and Challenger follow soon after, but it's too late for them; they disappear.

Finn awaits outside for the others to come out, she begins to see shadows of people that look like the others, but she's suspicious, so she takes to hiding. And it's for good reason she was suspicious a group of people exit the cave wearing Roxton, Marguerite and Challenger's clothes. They chat amongst themselves about how they are finally free, and that in two days no one would be able to send them back. While Finn in hiding makes the comment, 'no, he can't be here, he can't.'

The 'impostors' discover a map back to the treehouse in Challengers possessions, and head for the treehouse. Along the way, they are introduced to one of the plateau's other residents, dinosaurs. They make quick waste of the dino's and continue on, while meanwhile Finn beats them to the treehouse, and tries to come up with some form of a defense plan. While reaching for a rifle on a high shelf, she falls, and becomes unconscious.

The 'impostors' finally reach the treehouse, and discover Finn. They nurse her back to health and wake her, they make up a sorry excuse that they're actually explorers themselves looking for Challenger. But Finn knows better; pulls a crossbow on them, and makes her escape from the treehouse, saying to the Challenger impostor, 'your name is Zoth, I've seen you before.'

The impostors act dumbfounded at this revelation that Finn 'knows' the Challenger impostor, and the Roxton impostor heads off to capture her.

Zoth, and the Marguerite impostor now known as 'Una' discuss Zoth's plan to 'wreak havoc on the world, and to control the ones that survive the chaos.' Zoth also reveals that he wants Finn back so that he can send her into the fissure and bring back a demon named 'Salimyter' to assist him in his plans.

After going through Challengers journals Zoth devises a plan to bring chaos to the world using 'atomic fission bombs' delivered by remote controlled airplanes. (it's the most original idea since chopped wood!........)

Back in the jungle, the Roxton impostor catches up to Finn, after meaningless chit chat about how each would 'help' the other if they give themselves up, Finn continues running off, heading for the fissure. The imposter once again catches up with Finn, but she tricks him into thinking that she was headed another way, and comes up behind him. The impostor claims that if Finn kills him, then it will kill Roxton as well. Finn plans to send the Roxton impostor into the fissure in hopes that it will return Roxton. Along the way, Finn explains to the Roxton impostor that in her time (100 years in the future) Zoth destroys the world with bombs, chemicals, and radiation. Finn pushes the impostor on forward, but he falls; grabs a handful of dirt, and throws it in Finn's face to make his escape.

When the Roxton impostor returns to the treehouse, he learns of Zoth's plan firsthand, and doubt begins to show in him.

The impostors come up with a new plan to capture Finn. Just as Finn is about to burn down the treehouse with a flaming arrow, Una (Marguerite Impostor) runs from the treehouse while arguing with the others, as she retreats from the treehouse, Zoth and the Roxton Impostor fire shots at her, purposefully missing her. Finn scraps her plan to burn the treehouse down, and follows Una, Una sells Finn a story that she's jealous of another woman Zoth wants to bring back, and is leaving the group, just then, Zoth appears from behind Finn, and knocks her out.

While Finn is unconscious (again) we are shown flashbacks from when she was a child, watching TV of Zoth's reign of terror. When she wakes, the Roxton impostor is there, and explains that Zoth and Una intend to send her into the fissure to retrieve 'Salimyter.'

Finn and the Impostor group head for the fissure, along the way Finn and the Roxton impostor pull back from Una and Zoth, after Finn speaks a bit about the living conditions in her time, the Roxton impostor finally gives in, and lets her go. But Zoth and Una turn around just in time to catch them in the act, Una aims to fire at Finn, but the Roxton imposter jumps in front of her, catching the bullet himself. The impostor dies, and dematerializes, but in a few seconds Roxton materializes, and is alive!

Finn realizes she was fooled, and could have killed them anytime. She runs off to catch them, leaving Roxton behind, she catches up to them, and they exchange gunfire between one another, Una runs out; Finn shoots her, and Marguerite materializes.

But then Finn runs out of bullets, Zoth realizes this and runs for the fissure, Finn tries to pursue him, but Roxton comes out of no where, and holds her back saying 'it's too late,' Zoth makes it through the fissure void. Challenger emerges from the fissure only to have Finn greet him by saying, 'i could have saved the future, now all I've saved is you.'

Back to the treehouse, Marguerite is making another mental treasure map, counting out steps to where she'll hide her gems until the next way home presents itself. While Challenger examines Zoth's writings discovering how much his journals would have helped Zoth's cause.

Roxton, Marguerite, and Challenger try to convince Finn that since she knows what Zoth looks like, she can warn everyone else 'when' they get home, and the world will be ready for him. Finn takes the final line of the show with, 'if I'm here when he comes back, he's history.'