Toy company tycoon Milo Tieup is in a hotel room with his mistress preparing for a romantic tryst. While she is in the bathroom, a toy tank sneaks into the room through a doggie door, and shoots Tieup with a real bullet. Hammer and Doreau arrive at the scene, and question the mistress. Upon reporting back to Captain Trunk, Hammer accidentally let's it slip to Mrs. Tieup about her husband's affair. It turns out she was having her own affair with the company's lead toy designer, and that they were together when the murder took place. A short time later, the mistress winds up up dead as well having been killed in her bathtub by a toy submarine. Hammer and Doreau suddenly find themselves without suspects and a murderer still on the loose.

Trunk must solve the puzzle of why the army has surrounded the entire precinct before the entire staff dies.