George Bater owns a diner located near the 101 highway in California, and although he enjoys his somewhat isolated existence, he tires of the bickering between his staff, waitress Kotty and cook Slob. Kotty, who is dating Professor Sam Bastion, a nuclear physicist at a nearby laboratory, is irritated by Slob’s constant harassment. George, who secretly loves Kotty, reprimands Slob, a slovenly man who resents George for never calling him by his real name, Leo. Their latest quarrel is interrupted by the arrival of Sam, after which Kotty announces that she has been studying for the civil service exam. Kotty hopes to better herself in order to make Sam proud, although he tells her that he loves her as she is. Meanwhile, in the kitchen, Slob receives a shipment from commercial fisherman Perch, who sells him a small film canister, which Slob hides. George is cheered by the arrival of his pal, Eddie Miller, with whom he fought in World War II. Eddie, who has never recovered from the bloodshed he and George experienced during D-Day, is a traveling salesman. Although Sam presses Eddie to seek psychiatric help for his aversion to violence, Eddie protests that he has recovered from a minor nervous breakdown and is anticipating his upcoming vacation to Acapulco with George. Eddie and George plan their skin diving adventures, although Eddie grows queasy at the mention of harpooning fish. After Sam leaves, truck drivers Pepe and Artie enter and anger George by flirting with Kotty. Slob sneaks off to his room to look at the microfilm given to him by Perch, which contains secret formulas stolen from Sam’s lab. Later, as Kotty and Sam relax on the beach, Kotty complains that Sam does not spend enough time with her. Sam protests that he is busy with work, but Kotty, afraid that Sam is embarrassed to be seen with a waitress, becomes angry. The couple soon makes up, although Kotty is again angered when Sam ignores her to discuss seashells with Slob. After everyone else has gone to bed, Slob gives Sam the money he has received from selling the lab formulas, which Sam has secretly been supplying to Perch. Sam states that he is selling the secrets to a foreign government purely for money, while Slob confesses to wanting respect and power. Sam asks to meet Mr. Gregory, the head of the espionage ring, but Slob states that Gregory is not ready to meet him, even though Sam has been working for him for over a year. Slob then questions Sam about his relationship with Kotty, and Sam maintains that she is merely an excuse to come to the diner. When the misogynistic Slob threatens to “get even” with Kotty for refusing his advances, however, Sam orders him to stay away from her. Just as Sam is about to leave, Claude Dillon, a fellow scientist and spy, arrives, and drunkenly complains to Sam and Slob about the disappearance of another physicist, who is presumed to have committed suicide. Unknown to the men, as they try to dissuade Dillon from exposing their espionage, Kotty overhears their conversation and is horrified by the thought that her boyfriend is a traitor. After Kotty retreats to her room, Slob stabs Dillon in the back, much to Sam’s dismay, and has Perch drop the body in the ocean. The next day, Kotty confronts Sam, and when he does not deny her accusations that he is committing treason, she ends their relationship. Several days later, George attempts to comfort the depressed Kotty by asking her to marry him, but Kotty gently explains that she loves him as a brother. George is distracted by the arrival of Eddie with their skin diving equipment, and while Slob and Kotty watch George and Eddie stagger around in their swim fins, Pepe and Artie, who are really undercover intelligence operatives, search Slob’s room. Eddie gets nervous upon handling the harpoon, so George amuses him by acting out a charade of catching the stuffed tuna on the wall. Kotty sees Artie and Pepe leaving Slob’s room and mistakenly assumes that they are in league with Slob and Sam. When Pepe and Artie then enter the diner, carrying a newspaper bearing details of the discovery of Dillon’s corpse, Kotty is deeply frightened. The two men leave, after which George and Eddie depart for the market. Left alone with Slob, the impetuous Kotty reveals that she knows about his association with Sam and also tells him that she saw Pepe and Artie in his room. Meanwhile, as he is driving home, Perch is baffled to see Pepe and Artie meet Sam at a gas station and alerts Slob. Realizing that Artie and Pepe must be federal agents on his trail, and that Sam is working with them, Slob decides to escape and orders Perch to prepare his boat. Slob then reveals to Kotty that he is a foreign spy and attempts to kill her, but is interrupted by Sam's sudden arrival. Slob leaves the unconscious Kotty in her room and enters the diner, where he tests Sam by stating that Gregory wants to see him immediately. Sam agrees, after which Slob slugs him and snidely reveals that he is aware of Sam’s true allegiances. Kotty staggers out as Sam is admitting that he is in league with Artie and Pepe and has been investigating Gregory’s spy ring. Crying, Kotty embraces Sam, just as George enters. George is baffled to see Slob level a pistol at him and, not believing that Slob would hurt him, advances on him, only to have Slob shoot him in the shoulder. Slob proudly reveals that he is actually Gregory and states that he will force Sam to work for his superiors, as he has done with two other scientists. As Slob is stating his intention to kill George and Kotty, Eddie sneaks in and summons the courage to arm the harpoon and shoot Slob to death. While George comforts his shaken friend, Sam assures Kotty that he loves her. When George then spots Sam and Kotty kissing passionately, he sighs and adds a “waitress wanted” sign to the “cook wanted” sign he has just posted.