"Night Key" was a change of pace for Universal's horror star Boris Karloff. Playing largely horror related roles through most of the 1930's, this film offered him a chance to step out of that genre for a welcome change of pace.
Karloff plays mild mannered inventor David Mallory who lives with his daughter Jean (Jean Rogers), has invented a new "electric eye" security system. He had been cheated out of the profits of his previous wire based system by unscrupulous businessman and former friend Steven Ranger (Samuel S. Hinds). This time however, Mallory has also invented a "night key" system which disables his security systems.
Mallory's lawyer, Kruger (Edwin Maxwell) conspires with Ranger to cheat Mallory out of his rightful royalties for his new invention. With the help of petty crook Petty Louie (Hobart Cavanaugh) who he helps escape from Ranger's holding cell, the two set out to discredit Ranger's company. Meanwhile Ranger Officer Jim Travis (Warren Hull) tries to locate Mallory and in doing so falls in love with Jean.
Mallory using his "night key" disables the Ranger Security Systems of several business, taking nothing, in order to destroy consumer confidence in Ranger. A gangster, known only as "The Kid" (Alan Baxter) becomes interested in Mallory's invention. Petty Louie gives up Mallory's location thinking that the two will make some dough working for The Kid. The Kid has other ideas.
Karloff as always delivers a solid performance as the going blind inventor. No mad scientist here. The requisite romance between Rogers and Hull adds little to the story. Cavanaugh almost walks off with the film as the small time crook Petty Louie. Baxter is also good as The Kid. Ward Bond appears as one of Baxter's henchmen, Fingers. Also watch for long time character actor George Cleveland as Ranger's engineer and for "B" western fans, Roy Barcroft in an early bit as a Ranger technician.