This Universal programmer was based on a Collier's Magazine story by journalist Quentin Reynolds. This story in turn was ostensibly based on a true incident, in which a gangster "returned from the dead" to save an innocent young man from the electric chair. The nurse of the film's title is Katharine McDonald, who falls in love with her prizefighter-patient Lee Burke as he recovers from a beating received in a fixed prizefight. Katharine must fend off the advances of criminal attorney John Dodge, another patient who also loves her and becomes jealous of Lee. But when Lee is framed for the murder of his disgruntled manager, Slice, by a henchman of the fight-fix leader, Joe Largo, Dodge takes on his defense and works with Katherine to discover the real killer. Convicted and sentenced to death, Burke is about to walk the "last mile", as Katharine encourages mortally wounded Largo to a deathbed confession.

E.C.H.O., a secret organization with a strange name masterminds a bizarre plot to take over the world by dosing important `nerve centers' with super potent LSD. The only man who can stop them is Rex, a secret agent working for an undisclosed organization.