Peter is on the swim team, but can't keep up with the other kids. He claims its because he doesn't get the scissor kick, but the teacher won't listen to him. At home Judy tries to cheer him up and failing, decides to take him to Jumanji. Peter rolls and they get the clue "a machine will take you to the deep, but cannot tell you what to keep" before the two are sucked into the game again. There they find themselves surrounded by giant salamanders, but Alan manages to drive them off with a light bomb. Peter got some of the salamander slime on him without any notice. The three raid Ibsen's lab and steal his submarine, but Peter turns into a salamander. They're unable to find an instruction manual for the sub and are running out of air with Alan unable to figure out how to surface. Judy manages to hit a manual override and they surface near a desert island where Squint and two men are. Captain Squint reveals he survived the Draken attack, although it was a very near thing and ended up washed up on the island. Squint hijacks the sub and plans to use it to find a sunken city full of treasure and forces Alan, Peter and Judy to be his crew again along with his two men. Peter and Judy are forced to serve Squint's men while Alan is forced to help pilot the ship. They get attacked by a giant whale, but Alan drives it off with a torpedo. The pressure gets too much for the sub and Squint refuses to listen to reason, sending Judy and Alan into the back to fix a leak, but the sub breaks in half from the pressure. Alan and Judy get into scuba suits just as the part of the sub breaks completely and find nobody in the front half, but encounter a fully salamander Peter who is free. The demonic shark attacks them, but Peter and Alan manage to drive it off. Peter finds the treasure, but Squint attacks before Peter defeats him. Two demonic mermaids show up, but Peter warns Alan and Judy while Squint and his men fall into the trap and disappeared along with the treasure tower. Alan and Judy collect all the treasure left and find a balloon-like plant that can take them to the surface. They're forced to drop their treasure in order for it to work, because the treasure was too heavy. But they safely make it up, but have to retrieve Peter who turned back into himself. Judy realizes Peter solved the clue: the machine that took them to the deep was Ibsen's sub while what they needed to keep was the ballon plant as it was able to take them back to the surface. Clue solved, the two return home, leaving Alan to swim to the nearby island for coconuts and crabs Squint and his two mates had. At home, Peter is now the best swimmer on the team due to his experiences as a salamander teaching him better swimming techniques.