West and Gordon are in San Francisco to meet an old friend, Lt. Bartlett of the U.S. Navy, who has discovered something he doesn't feel he can reveal to his superior, Admiral Hammond. Unfortunately, Bartlett is killed by what appears to be a gigantic sea monster before he can reveal his secret. Ignoring a local preacher's ramblings about the "coming of Leviathan," West goes out to sea and manages to cut off a piece of one of the creature's tentacles - which turns out to be made of rubber. Meanwhile, Gordon uncovers a new type of diving apparatus which Bartlett invented and then concealed. The agents decide to reveal their findings to Hammond, but a bomb silences him just as he decides to trust them; however, the explosion reveals something in his office - a hidden model of an underwater fortress. Together the agents must make their way to the bottom of the sea and expose the truth behind the myth of the kraken.
Tropes present in this episode:
- Boisterous Bruiser: Jose Aguila, spokesman for the Portuguese fishing community, is pretty upset about a fishing embargo which has been put in place, but otherwise he's an enthusiastic, outgoing and rather large guy who gleefully helps Jim dispatch a gang of thugs.
- Combat Tentacles: The sea monster uses gigantic tentacles to attack Bartlett, Jim and any fishermen who happen to be out in the bay.
- Crazy Homeless People: Daniel, the "seagoing preacher" who raves about Leviathan to anyone who will listen.
- Kraken and Leviathan: There is one supposedly terrorizing the San Francisco waterfront, but it turns out to be just a Scooby-Doo Hoax.
- Mugged for Disguise: Artie takes out the bad guys' mechanic and then disguises himself in the mechanic's clothes.
- Obfuscating Insanity: Daniel. His insane ramblings about the coming of Leviathan are only a cover; he's actually helping to run the whole "fake sea monster" operation.
- Scooby-Doo Hoax: There's no kraken. It's a fake created to scare people off and keep them from finding out what's really going on at the bottom of the bay.
- Tuckerization: In the tag scene, Jim and Artie talk about a friend of theirs, a soon-to-be-married playboy millionaire called Irving Moore - named after the show's most frequent director (though not of this episode).
- Underwater Base: The whole point of the "kraken" is to conceal the construction and operation of one of these off the coast of San Francisco.
- Unwitting Pawn: Admiral Hammond is being manipulated by his wife, who wants to co-opt his underwater fortress for her own purposes.