Frustrated with Zoidberg's incompetence as a doctor, the Planet Express crew starts a labor union mob, betray Zoidberg and rudely demand Professor Farnsworth to fire him. The professor refuses, and the crew question why Zoidberg was ever employed in the first place. A series of flashbacks reveal that Zoidberg first met and befriended Farnsworth in 2927, during a mission to kill a Tritonian yeti for Mom's bioweapons research. As they parachute out of a spacecraft, Zoidberg asks Farnsworth if everyone had taken their hypermalaria pills. After setting up camp, Zoidberg determined that everyone but himself had contracted hypermalaria, a fatal, incurable disease which can either strike instantly or remain dormant for years. With all of Mom's mercenaries doomed to die as well as himself, Farnsworth decides to kill the yeti himself. Zoidberg chased after him and together they killed the yeti. As a favour to Farnsworth for killing the yeti and saving his life, Zoidberg agrees to an arrangement: when Farnsworth begins to experience symptoms of the disease, Zoidberg will have to perform a mercy killing before the disease can fully manifest. As a result, Zoidberg was employed by the professor for the sole purpose of carrying out this task.
In the present, the professor begins to experience the symptoms of hypermalaria. The Planet Express Crew enters Zoidberg's office in a mob fashion and starts yelling at him and bullying him. Professor Farnsworth tells Zoidberg to come to his office, and the crew thinks that the Professor is going to fire Zoidberg. The Professor instead tells Zoidberg that the hypermalaria is starting to kill him after 80 years, and insists that Zoidberg must kill him by surprise because Farnsworth prefers it that way. Zoidberg attempts to kill the professor multiple times but all the attempts fail and backfire. The crew catches Zoidberg attempting to mercy kill the Professor, and restrain him with the professor's lab coat, then imprison him in his own office. Zoidberg cuts himself loose from the coat and then notices a single white hair on the professor's coat. Upon examining it, he has a revelation.
Meanwhile, Farnsworth berates his employees for their interference and explains about his arrangement with Zoidberg. The crew returns to Zoidberg's office to free him, but he had already escaped from his office prison by "sandcrabbing" his way out. Zoidberg goes to Mom's, exchanging a coupon for a free tanning session for the "thing" from Triton.
Back at Planet Express, the crew decide to kill Farnsworth themselves, using an elaborate and way overdone mechanical Rube Goldberg killing machine called The Murdolator. The machine works with a wheel covered with axes on a metal grid that surrounds the room. The crew each take a bottle of cyanide to add to the wheel to share the guilt, which is called a killcheck. There are six killchecks in all and when all of them are performed, the professor will die. Hermes performs the first killcheck and Fry performs the second killcheck. When Bender performs the third killcheck and makes a delicious salad in the process, Zoidberg returns. Leela and the entire crew apologize to Zoidberg for mistreating and imprisoning him and tells him that they are killing the professor for him. However, Zoidberg reveals that the professor doesn't have hypermalaria, but rather, he has contracted yetiism after being scratched by the Tritonian yeti. The illness mimics the symptoms of hypermalaria, but instead of dying in the last stage, results in its victims transforming into a yeti.
As the crew restrains Farnsworth, Zoidberg brings a yeti head out of a box and extracts its pineal gland, which he intends to use to cure the Professor by neutralizing the adrenal neural toxin, which prevents yetis from driving themselves mad. But as his friend starts getting out of control, Zoidberg forces him to swallow the yeti gland. At first, it turns him into a double-yeti, before the Murdolator collapses on him. And from the rubble, Farnsworth emerges, successfully cured. As the crew goes to a tanning salon to celebrate, Zoidberg laments giving away his coupon. A grateful Farnsworth offers to treat Zoidberg to a free session, and they both depart as friends.