Many Alcatraz prisoners have volunteered to take an experimental serum that could cure a fatal blood disease, promised parole if they take part. During the experiments, notorious racketeer Barry Morgan steals one of lieutenant nurse Joan McKenna's scissors and stabs convict Eddie Ganz to death, then escapes.
The medical tests are abandoned, and the vaccine is called a failure. Joan is upset for many reasons, including that such a serum could help her brother Dick, who has the disease. Dr. Ross Williams created the medicine and he attempts, with Joan's help, to understand why Morgan behaved the way he did. Ross is beaten by one of Morgan's thugs, Duke Shaw, and told that he and Joan had better drop their pursuit, but they don't.
The trail leads them to Lake Tahoe and a lodge owner, Ethel Ganz, the dead inmate's stepdaughter. She pulls a gun on them. It turns out Eddie hid $250,000 in stolen loot that she found. Ethel is now married to Morgan, with whom she plotted the murder and prison breakout. Morgan turns up with a gun, putting the lives of Ross and Joan in peril, but she is rescued, the villains are incarcerated and the serum is put to good use.
