A Federal Agent goes undercover in prison to break up a drug syndicate.

In jail, convict Henderson expects to be freed, but his cellmate, Quinn, decides to break out on his own. Quinn goes to the home of Arnold, a member of a dope smuggling gang, whose daughter Julie treats Quinn's wounds. Arnold, whom the Secret Service believes is a potential informer, is warned by another agent that the gang is about to be rounded up, and Arnold's nurse and maid reports this information by telephone. Henderson, having been released from prison, goes to Dr. August Steiner, who tells him to take over from Arnold. Burt has followed Henderson to Steiner's office, and Steiner orders Henderson to kill Burt. Captain E. J. Hawkes, meanwhile, summons a meeting of a citizen's committee that is headed by the respected Dr. Alec Munsell. Hawkes anticipates the arrest of the gang, but then learns that Burt has been killed. Quinn has become Arnold's chauffeur, and he and Julie are in love. While visiting Henderson, Steiner recognizes Quinn as Jack Hart, another Secret Service man working undercover. Henderson is told to have Jack fly in the next shipment, then have him killed. After Jack tells Julie that her father is involved in a most unsavory business, she learns from him Jack's true identity. When Julie learns of Jack's fate, she tries to warn him, but is too late. Henderson orders Jack to ditch his plane and bail out by parachute, then abandons him 200 miles offshore. Meanwhile, a concerned Julie goes to Hawkes and learns that, by dumping a dummy attached to a parachute Jack tricked Henderson and is still alive. Upon returning to arrest Arnold, Jack and Hawkes find a note that Arnold has been admitted to the Eastland hospital. Arnold dies, after which Jack hides Julie at the Hotel Ansonia, then goes to Steiner's office. There, Jack finds a hidden dictaphone whose cylinder he takes. He then suggests an autopsy of Arnold's body, and late at night, they bring the casket to Munsell's home. However, upon opening the coffin, they find it full of narcotics. Jack leaves, then finds Julie sick at the hospital, where he is taken prisoner himself. He awakes on the operating table, where Steiner is about to perform surgery on him without an anesthetic. Julie, having recovered, enters and shoots Steiner, who is actually Munsell in disguise.