On his way home, police officer Robert Rawlins stops a man about to burglarise a radio and television shop. The burglar shoots Rawlins and escapes. The cops find clues in the burglar's car. Police captain Breen says, "It looks like some kind of electrical device. United States Navy. It's either stolen or war surplus." Or maybe the shooter's in the Navy!
Based on Rawlins' description of the shooter as a moustachioed white male in his twenties, the cops sweep the streets and arrest many including a clean-shaven elderly Chinese man. Don't they have better things to do, like solve murders? Oh wait, they do! Mrs. Rawlins' hospital vigil ends when she's notified she's a widow.
Breen assigns Sergeants Marty Brennan and Chuck Jones to the case. The shooter used a stolen a car and left no fingerprints. Lee the crime lab technician declares the shooter smart and knowledgeable about electronics. Everyone acts baffled. Why don't they follow the clue and check with the Navy? Why do I insist on giving advice to people in a movie?
The shooter lives with his small dog. Roy Martin (the shooter, not the dog) steals equipment and sells to an unwitting supplier, Paul Reeves. When a customer recognises a piece of Reeves' equipment as stolen from him, Brennan and Jones persuade Reeves to arrange a meeting with Roy. But his anxiousness tips Roy off. Brennan and Jones lie in wait at Reeves' office. Just the two of them. There's been a sudden shortage of manpower at the LAPD. Jones clumsily gives them away. Roy overcomes Brennan and shoots Jones. Roy escapes but sews up his own bullet wound in a long and queasy sequence.
Breen learns that Jones may be paralysed for life. The cops are suspicious of Reeves and put him under surveillance. Reeves says Roy was attached to a radar unit in the war. It's a clue! It's ignored! It's this movie, that's why! Roy crosses over from burglary to the fast-growing industry of robbing liquor stores. Lee the lab tech finds a match between bullets from the Rawlins and Jones shootings and the robberies. The cops build a composite sketch of Roy based on witness accounts of the liquor store robberies and send the sketch everywhere. Except the war department, that is.
Roy slips by the cops watching Reeves' house. He beats up Reeves and steals Reeves' money. Breen is disappointed that Roy escaped. Brennan is disappointed he's been working the case for months. Months! Breen takes Brennan off the case. Brennan visits Jones and sulks over his dismissal from the case. Jones doesn't feel sorry for Brennan. I wonder why. Brennan whines that the case is tough and wishes that Jones would help him. Jones is so selfish. He's only ever been shot, after all. Jones says if he could, he'd boot some sense into Brennan. Funny, I have the same wish. Jones says if it seems like Roy knows how the cops operate, maybe Roy's a cop. Brennan stops sulking and searches all the police departments. Someone recognises Roy as having worked as a radio technician in their department before the war.
A postman recognises Roy from his delivery route. Brennan dresses up as a milkman and delivers milk to the residents in Roy's apartment. What does that have to do with cracking the case? Yes, indeedy. Brennan identifies Roy from the sketch. Does he arrest Roy then and there? Brennan's only ever twice the size of Roy. No, Brennan returns to the police station. Presumably after he ends his milk run.
Breen and Brennan make plans to storm Roy's place at night. Luckily Roy hasn't run away yet because he would have a ten-hour lead on the cops. Roy's dog alerts him to the cops. Roy escapes into LA's underground storm drain network. The cops pursue him. In a shootout, Roy is killed.