While Gilligan is catching lobsters he thinks he sees a sea monster. He rushes to tell everyone. When he's gone we see it's a submarine with a Japanese sailor inside. Professor and Skipper don't believe him. Gilligan goes back to the lagoon and tells Thurston who also doesn't believe him. The soldier captures Thurston thinking he's an officer. Gilligan claims that he was eaten by the sea serpent. Gilligan and Ginger head back to the lagoon to look for Thurston but Ginger is captured too. Lovey is then captured. Gilligan goes back to the camp to warn the Skipper. Skipper and Gilligan go back to find the Professor but he was captured too. The women and men are in different cages guarded by the Japanese sailor.
professor tries to explain to the sailor that World War II is over. But the sailor doesn't believe them. Nor did he hear it on the radio or transmitter because they broke in 1942.
Skipper and Gilligan find the Japanese submarine. Skipper can't believe it. Skipper tries to fit into the submarine opening but he gets stuck. Gilligan uses coconut oil to get him out. Gilligan has to drive ths submarine to get help. He climbs in but doesn't remember to close the hatch. Gilligan hits land thinking he's in Hawaii but he didn't even leave the lagoon. The main problem is that all the directions and controls are in Japanese.
The Professor and Thurston try to negotiate with the sailor but it doesn't work. Ginger flirts with him in hopes to get released. The sailor falls asleep in a tree. Skipper goes to dig the men out because the cage is rigged with grenades. Gilligan climbs up the tree taking the cage keys and the gun off the sailor. He unlocks both cages. Everyone is free. The soldier has vanished to his submarine. He starts driving in an erratic pattern because he can't see where he's going. Gilligan also took his glasses.