While on a rescue mission in a shuttle outside of the seaQuest, Henderson, Lucas, Brody, and O'Neil start to get pulled into an underwater whirlpool. After a crash landing, the four of them find themselves in a mysterious cavern, where they meet a scientist, Rollings, who also found himself trapped.
They managed to escape sever injuries from the crash landing, but O'Neil did manage to break his leg. The team soon realizes that their only hope of escape is to design a new submersable with different parts from each of their shuttles.
Much to their dismay, however, Lucas calculates that they will only have enough oxygen for four people, so one of them will have to stay behind. They decide to work on building their escape plan before holding a lottery to decide their fates.
On board the SeaQuest, Darwin opts to help find the missing team, and Bridger, fearful for Darwin's life, reluctantly agrees. Lucas manages to design their new submarine, and the team gets to work on building it.
They are interrupted by a rumbling sound, which turns out to be a fire-breathing worm. Luckily, Brody saves the day by shooting fire back at the worm, who slides away, momentarily defeated.
Lucas' design works perfectly, and it is time for the lottery. Eventually, Lucas ends up with the short straw, and, accepting his fate, walks off to be by himself.
Henderson, worried, follows Lucas, and asks him if there is anything he wants, or if he wants to be with her. He asks her to hold him until he falls asleep, and she agrees.
Meanwhile, Darwin manages to pinpoint their location, and tells Bridger. Smith manages to sense Lucas, and runs to tell Bridger that the team is indeed alive.
Back in the caves, the water begins to rise, and everyone dashes for the submorine. Rollings, however, decides to give his spot to Lucas, so Henderson, Brody, Lucas, and O'Neil head off in the submersable.
After a very rough time, they manage to make their way out of the hole, but are unable to rise to the surface. The SeaQuest, however, rushes in to rescue them. Once on board, Lucas rushes to the Stinger to go back and save Rollings. Dagwood accompanies him. Lucas manages to get all the way back into the cavern, and get Rollings. The giant worm, however is on their tail. As they burst throug the opening, the SeaQuest laser blasts the worm, which dies immediately.
Lucas manages to pay Rollings back for saving his life after all.