At the Presidio, a military base in San Francisco, California, Military Police officer Patti Jean Lynch arrives for evening patrol. She drives to the Presidio Officers Club and sees a silver Lincoln car. Noticing the club’s door open and hearing voices inside, she draws her gun and enters. Inside a storage room, two men shoot and kill her before escaping in the Lincoln. Afterward, San Francisco Patrolmen Schmidt and Dotson see the speeding Lincoln and chase it. The killers shoot the police cruiser, causing it to crash, killing the patrolmen. Later, San Francisco Police Inspector Jay Austin is called into his lieutenant’s office, and assigned to investigate the shooting at the Presidio. Austin, the lieutenant believes, is the best candidate, since he was stationed at the Presidio as an M.P. before joining the San Francisco police department. At the Presidio, Jay runs into his friend M.P. Zeke, who tells him the victim is Patti Jean Lynch, Jay’s former partner. Jay finds Lt. Colonel Alan Caldwell, Presidio Provost Marshal, and Jay’s former commanding officer. Jay informs Caldwell the city police will take over the investigation. Caldwell warns Jay not to cross him while he is on the base. After Caldwell leaves, Jay notices a potted plant filled with water. The next morning, he arrives at Lt. Colonel Caldwell’s home. Caldwell’s adult daughter, Donna Caldwell, invites him in. Jay asks Donna to join him for dinner, and she agrees. He informs Caldwell that a Russian Tokarev pistol was used in the murder, and asks Caldwell to accompany him as he speaks to the head of the base firing range, Sergeant Garfield. He wants to find out if anyone on base has a Tokarev pistol. They drive to the Presidio. Sergeant Garfield recently repaired a Tokarev for Colonel Paul Lawrence, a high-ranking officer on base. Back at his home, Caldwell reads Colonel Lawrence’s file, as Donna gets ready for her date with Jay. He attempts to dissuade Donna from dating Jay. He tells her that as M.P.s, Jay and Patti Jean Lynch pulled over an intoxicated Colonel Paul Lawrence, and that Jay beat him up before arresting him. Donna would like to hear Jay’s side of the story. Unsatisfied with her response, Caldwell forbids her from going out with Jay. Not caring, Donna leaves. At dinner, Jay tells her about punching Lawrence once after he resisted arrest and was belligerent to Patti Jean. Caldwell sided with Colonel Lawrence because he was a superior officer, and Jay quit the army shortly thereafter. Donna suggests they leave and spend time together. Jay follows Donna in his car. However, Donna begins driving erratically and Jay loses her. When he parks at his apartment, he finds Donna waiting. They kiss, and Jay carries her inside. The next day at the Presidio, Jay and Caldwell meet with Colonel Lawrence. Caldwell requests Lawrence turn over his pistol, but Lawrence says he lost the gun in a poker game. When Jay asks who won the gun, Lawrence orders Jay out of his office. Caldwell and Jay go to the shooting range and ask Sergeant Garfield if he fired the gun after repairing it. Garfield says yes and finds a bullet for them to compare with the one that killed Patti Jean. Before leaving, Jay invites Caldwell to join him as he interviews Arthur Peale, a businessman who reported his silver Lincoln stolen. Caldwell instructs Jay to pick him up at the Presidio Army Museum later. At the museum, Sgt. Major Ross Maclure gives a tour to some school children. Caldwell interrupts and tells the children about Sgt. Major Maclure’s saving his life during the Vietnam War and being awarded the Medal of Honor. After the children leave, Caldwell tells Maclure about working with Jay again, and his unhappiness over Jay dating his daughter. Arriving at Peale’s company, Transcorp, Jay and Caldwell meet Peale and his assistant, Mark. While Jay speaks to Peale, Caldwell notices bar coasters from Saigon, Vietnam, on the table. Afterward, Caldwell and Jay go to a bar for a cup of coffee. A man at the bar bothers Caldwell by calling him “Major,” and Caldwell knocks the man unconscious. Later at the Officers Club, Caldwell looks once again in the storage room for clues, and finds one open water cooler bottle. Meanwhile, Jay receives a call from M.P. Zeke, informing him that Colonel Lawrence is in Chinatown. When Jay informs Lawrence that a bullet fired from his pistol matched the one that killed Patti Jean, Lawrence hits him and runs away. Jay gives chase, but Lawrence is struck and killed by a yellow sports car. Later, Caldwell arrives at the scene and finds Jay. He ran a background check on Peale, and learned that he previously worked for the Central Intelligence Agency (CIA), and was stationed in Vietnam during the time Lawrence was there. Caldwell also tells Jay about the open water cooler bottle, and Jay recalls the one watered potted plant he saw that night. At Black Mountain Spring Water, Inc. the following day, Jay flirts with the delivery dispatcher, Gloria, and obtains Presidio Officers Club deliveryman George Spota’s name and address. Caldwell tells Jay a man named George Spota served as Master Sergeant under Colonel Lawrence in Vietnam. Later, Caldwell calls a friend at the CIA and learns that Arthur Peale owns Black Mountain Spring Water, Inc. Meanwhile, Jay arrives at George Spota’s house and sees a recently-painted blue sports car, and discovers it was the yellow car that killed Lawrence. That evening, Jay accompanies Donna to a military banquet at the Presidio Officers Club. In front of Jay, Donna openly flirts with Captain Gordon. Frustrated by her lack of commitment, Jay punches Gordon and breaks up with Donna. Afterward, Caldwell finds Donna at home and she yells at him for trying to control her life. She goes to Jay��s apartment to apologize for pushing him away, and tells him she loves him. Elsewhere, the inebriated Caldwell arrives at Sgt. Major Maclure’s house, and climbs the fire escape to his window. Maclure and Caldwell climb to the roof and reminisce about their friendship through the years. The next day, Caldwell informs Jay about Peale owning Black Mountain Spring Water, Inc. In response, Jay states that George Spota killed Lawrence. The men trail Spota to Travis Air Force Base in Fairfield, California. There, he picks up a full water cooler recently arrived from the Clark Air Base in the Philippines. Jay and Caldwell assume the bottle contains smuggled goods, and that Spota delivered the wrong water to the Presidio Officers Club by mistake. Patti Jean Lynch caught him, and she was killed. Later, they follow Spota back to the water company and see him carry the Philippines water bottle inside. They see Sgt. Major Maclure enter the warehouse as well. Caldwell and Jay break into the bottling plant. Inside, Arthur Peale pours water from the bottle through a food strainer and reveals a number of diamonds, invisible in the water. Maclure arrives with a gun and tells Peale the operation is over. Peale attempts to reason with Maclure, stating it had been Lawrence, not Peale, who had blackmailed him into participating. Not caring about the consequences, Maclure states he is turning himself in. However, one of Peale’s associates knocks Maclure unconscious. Suddenly, Peale and his associates hear the building’s alarm and run. Caldwell and Jay find the empty bottle with the diamonds as Peale’s men shoot at them. Maclure regains conscious and goes after Peale. However, Peale’s assistant, Mark, shoots Maclure, making him drop his gun. Jay shoots Mark in the chest, killing him. Meanwhile, Caldwell finds Maclure as Spota shoots at him. Maclure runs for his gun and tosses it to Caldwell as Spota kills him. Caldwell kills Spota, but is fired upon by Peale. However, Jay shoots Peale, and kills him. Afterward, Caldwell asks Jay not to file a police report for two days so Maclure can be buried with his name and honor intact. Jay agrees. Days later, Caldwell speaks at Maclure’s funeral. After the service, Caldwell reconciles with Donna and accepts her relationship with Jay.