A gang of criminals, which includes a piano player and an imposing former convict known as 'Gruesome', has found out about a scientist's secret formula for a gas that temporarily paralyzes anyone who breathes it. When Gruesome accidentally inhales some of the gas and passes out, the police think he is dead and take him to the morgue, where he later revives and escapes. This puzzling incident attracts the interest of Dick Tracy, and when the criminals later use the gas to rob a bank, Tracy realizes that he must devote his entire attention to stopping them.
Boris Karloff
as Gruesome
Ralph Byrd
as Dick Tracy
Anne Gwynne
as Tess Trueheart
Edward Ashley
as Dr. L.E. Thal
June Clayworth
as Dr. I.M. "Irma" Learned
Lyle Latell
as Pat Patton
Tony Barrett
as Melody
Skelton Knaggs
as X-Ray
James Nolan
as Dan Sterne
Joseph Crehan
as Chief Brandon
Milton Parsons
as Dr. A. Tomic
Ernie Adams
as Waiter at Hangman's Knot (uncredited)
