Amy and Leela drag Fry and Bender to the gym, and Doctor Zoidberg tags along. While at the gym, Zoidberg behaves erratically, unusually and aggressively, and even develops a head fin. Back at the laboratory, Professor Farnsworth examines Zoidberg, whose claws are held shut with rubber bands, and determines that it is mating season for Zoidberg's species.
The crew flies to Zoidberg's home planet, Decapod 10. After a short tour, Zoidberg sets up a mound on the beach and begins trying to attract a mate. After an unsuccessful day, Zoidberg meets Edna, an old classmate. She rejects him and Zoidberg leaves depressed and upset.
Fry begins teaching Zoidberg how to win Edna's heart using human romance techniques. Using his newfound techniques, Zoidberg successfully woos Edna to a date. While at a restaurant, Leela reveals to Edna that Fry is responsible for the change in Zoidberg.
Under the pretext of discussing Zoidberg, Edna invites Fry to her apartment and begins an unsuccessful attempt at seducing him. Zoidberg walks in, sees them embracing, starts to think that Fry has double crossed Zoidberg by sweeping Edna off her feet, and challenges Fry to Claw-Plach, a ritual fight to the death.
In the arena, Fry is about to defeat Zoidberg, but cannot kill his friend. Unfortunately, Zoidberg doesn't feel the same way and cuts Fry's arm off with his claw, prompting Fry to curse Zoidberg before proceeding to beat him with his severed arm. After more fighting, Fry and Zoidberg look up to discover the entire Decapodian audience has left, including Edna who has decided to mate with the emperor. Once every Decapodian is underwater, masses of eggs float to the surface; Zoidberg has missed the mating frenzy of his species. They soon witness the corpses of all the Decapodians float to the surface, where they are feasted on by seagulls. Zoidberg explains that members of his species die after mating and apologizes to Fry about how he acted. He felt things he never felt before: "love jealousy, and passion for disemboweling". He then tries to reattach Fry's arm but he attaches it on the wrong side. Trying again, he saws off the legs. For the last try it is presumed, since there is no scream of pain audible, that he beheads Fry.
The episode owes much to the September 17, 1967 "Amok Time" episode of Star Trek: The Original Series in which Mr. Spock returns to his homeworld Vulcan for a brutal Vulcan mating ritual.