Trama

An impostor posing as Mr. Howell claims to having been rescued and begins selling off Mr. Howell's stocks. The real Mr. Howell offers his fellow castaways a hefty reward to get him off the island and save his fortune.

Listening to the Radio, Mr. Howell (Jim Backus) hears that he is about to be interviewed, but he soon begins to realize that it is an impostor (Also played by Jim Backus) impersonating him. The impostor claims that he alone of the seven castaways had survived the sinking of the S.S. Minnow. The impostor's intentions are obvious as he begins to spend Mr. Howell's fortune and sell off his company stock-by-stock to fund his lifestyle. The real Mr. Howell wants to stop him. Every time he hears of the phony Howell spending or selling his property, he goes berserk and runs to the lagoon as if he was going to swim back to the mainland. The Skipper (Alan Hale Jr) and Gilligan (Bob Denver) stop him each time. However, his worries are dispelled as the radio reports the phony Howell has fallen overboard from a boat while sailing and is reported lost. A search is on the way for the man still believed to be Thurston Howell III, and by the following day, the impostor somehow manages swim ashore onto the Island. Wandering the island, he is shocked to discover the real Thurston Howell sitting in his chair. Knocking him upside the head with a coconut, he renders the real Mr. Howell unconscious and drags him into the jungle, changing clothes with him in an attempt to fool the other castaways. Eventually, the real Mr. Howell regains consciousness in the impostor's wet clothes and heads back to his chair, discovering the impostor and calling out to the others and Ginger (Tina Louise) and Mary Ann (Dawn Wells). Only Gilligan, the Skipper, and Mrs. Howell (Natalie Schafer) come on the scene, and he tries to convince the others that he is the real Thurston Howell. The impostor, however, rebuffs all his responses with "Howell-like" responses and a similar mole to the real Mr. Howell on his elbow. Fortunately, the Professor (Russell Johnson) shows up with the radio with the latest update on the impostor, who has been proven to be a fake when earlier signatures of the real Mr. Howell are compared. His ruse discovered, the phony Mr. Howell slips away to the lagoon with the Castaways running after him. As he swims away from the island, the Castaways stop chasing him at the edge of the water. The Skipper tells Mr. Howell that he won't be able to spend anymore of his money, but Howell disagrees as the impostor is wearing his clothes with his money and credit cards in the back pocket, so he dives into the lagoon once more to get them back. A few days later, news comes over the radio that the impostor has been picked up by a fishing boat and apprehended. Meanwhile, Gilligan wonders if the fake mole on the impostor could have been painted on and tries checking Mr. Howell who shoos him off. However, that just spurs suspicion in Mrs. Howell who tries checking his arm herself.