The Invasion

"The Invasion" is the 79th episode of Gilligan's Island and the eleventh episode of the third season.

Synopsis
Gilligan pulls in a military briefcase from the lagoon that incites the curiosity of the Castaways trying to look inside it. They try various stunts to take the case and peek inside, but the Professor foils each of them. The following morning, the case has vanished, having been passed one by one covertly through the Castaways trying to hide it until Gilligan gives it back to the Professor, who pounds it in disgust only to discover it has secret military papers in it. Gilligan hand-cuffs himself to it to protect it, but the Skipper realizes Gilligan would be killed when the men after the case find him with it. That night, he has a dream he's a secret agent, and everyone is a spy trying to get the briefcase with Mr. Howell as the head of the evil organization after it. When Gilligan wakes from a start after the dream, Mr. Howell comes running and scares him, opening the case and revealing the key to the cuffs. The files, however, turn out to be from World War One, which means no one would be after them after all. Deciding to toss the briefcase back into the lagoon, Gilligan tells the Skipper and Professor about his dream, adding that the Skipper was an imposter of his mother, the Professor was the head of the good guys and that the briefcase was rigged to explode. Upon tossing it, it really does explode, surprising them.

Trivia

 * The syndicated versions of this epsiode delete the tag scene where Gilligan remarks on the briefcase self-destructing and the resulting explosion.