Just out of jail, Gruesome goes to the Hangman’s Knot saloon, where his old crime crony Melody is now playing the piano in a honky-tonk. Gruesome takes him to a plastics manufacturer, where X-Ray and a mysterious mastermind are in possession of a secret formula and hatching a sinister plot.
Ignoring a warning not to touch anything, Gruesome sniffs a nerve gas that paralyzes him. He appears to be dead and is taken to the city morgue.
Dick Tracy is at headquarters speaking with college professor Dr. Tomic, a scientist who suspects someone has been following him. At the morgue, Tracy’s sidekick Pat has his back turned when Gruesome wakes up and knocks him out. Pat describes him to Tracy as looking a lot like the actor Boris Karloff.
At a bank where Tess Trueheart happens to be, Gruesome and Melody use the nerve gas to incapacitate the customers and security guard. They rob the place of more than $100,000 and shoot a cop on the sidewalk before Tracy and his men arrive. Gruesome demands half of the loot from X-Ray …. or else.
Tracy tries to learn the secret of the formula from Dr. Tomic’s top assistant, Professor Learned, before going after Gruesome and his gang. It all ends in a shootout, with Gruesome shot by Tracy, and then back at headquarters, where Tracy ends up frozen by nerve gas just as he’s about to kiss Tess.
- Ralph Byrd as Dick Tracy – The tough, square-jawed detective
- Anne Gwynne as Tess Truehart – Tracy’s girlfriend, who witnesses the bank robbery
- Boris Karloff as Gruesome – A corpse-like gangster.
- Skelton Knaggs as Rudolph X-Ray – Gruesome’s spectacled henchman
- Edward Ashley as Dr. Lee Thal – an interested party.
- June Clayworth as Dr. I.M. Learned – Prof. Tomic’s assistant
- Lyle Latell as Pat Patton – Tracy’s bumbling sidekick
- Tony Barrett as ‘Melody’ Fiske – A greedy, piano-playing thug
- James Nolan (actor) as Dan Sterne – A nosy newspaper reporter
- Joseph Crehan as Chief Brandon – Tracy’s reliable boss
- Milton Parsons as Dr. A. Tomic – a State U. physicist