Plot

A war among gambling bosses is being waged. Stone and Keller attempt to locate and protect a vital witness from a hit man who has charmed his way into a lonely schoolteacher's apartment in order to secure a clear shot at his victim.

The Chafee Brothers are numbers runners in San Francisco. When big shot gambling boss Hoyt Llewelyn starts muscling into Roy Chafee's territory he decides to go to the police and meet Mike Stone and Steve Keller at an arboretum. His brother Frank meanwhile continues running numbers and stops at a bar next to a small store. While Frank is inside Arthur Styles, a hit man, wires a trigger mechanism with shotgun shell to the ignition of Frank's car unobserved by passerby. Frank accidentally strikes a lady with groceries - Mary Rae Dortmunder, a high school teacher. After helping her pick up her spilled groceries Frank gets into his car and is shot by the trigger mechanism

Hoyt now tells Art to stake out the apartment if Roy Chafee. The place is across the street from another apartment and Art charms the tenant in the apartment with the best shooting view of the Chafee house - which happens to be that of Mary Rae Dortmunder. Though taken aback (as as yet unaware he is a wanted criminal), Mary Rae is lonely enough to accept Art Styles into her place.

Upon learning of Frank's murder Mike orders Steve to tail Art Styles' car; Steve thus learns Styles is staying with the school teacher, but.neither as yet knows of the stakeout of the Chafee apartment since only Roy's wife is there. Mrs. Chafee doesn't know where Roy is hiding but she is due to give birth in a day or two, and the two cops stake out her place believing Roy will show up to support his wife and the arrival of their child. Mike for his part had confronted Hoyt and his partner Abby Groat about the Chafee killing and warned them to stay away from Roy Chafee - and drops a hint of a possible double cross, which winds up disturbing Abby enough when Hoyt boasts about tapping Frank's phone for a year.

After getting a phone call from Art staked out at the Dortmunder place Hoyt drives to a dockside meeting with Abby that night - only to find his car has been sabotaged by Groat. Hoyt thus is thrown in his car into the harbor. After the car and Llewelyn's body are dredged out, Mike and Steve thus must follow Mrs. Chafee when she gets a cab to a pay phone to call Roy. This of course smokes out Roy and a three-way chase soon develops between Art Styles (with Mary Rae briefly a hostage), Mike and Steve, and Abby Groat and one of his gunmen.