A cop is killed and a mob boss is wounded in a shoot-out at a nightclub where young Dr. Tom is dining with his bride-to-be, Mary. After being asked to treat Boss Grusso's injury, Tom is approached by police to go undercover as the gang's "in-house" physician in an effort to bring them to justice. Tom's new secret life puts a strain on his relationship with Mary, and he's determined to get out of the dangerous assignment. The police chief, sensing a break in the case, convinces Tom to stay on. Neither of them is aware that Tom's cover has already been blown, and that Grusso and his thugs have laid a deadly trap.Richard Cromwell followed up his Riot Squad performance as Dr. Tom with the title role in the 1942 gangster film, Baby Face Morgan. Screen veteran John Miljan, Riot Squad's oily mob boss, appeared in 200 films in his three decade career, most memorably as General Custer in Cecil B. DeMille's 1936 Western classic, The Plainsman. Riot Squad also marks the last screen appearance of eight year old Mary Ruth, once tagged as "the next Shirley Temple," seen here incongruously interrupting the crime drama with a song.
