When popular, egotistical movie detective Willard "Bill" Martin states publicly that he could do a better job of solving murder cases than the Los Angeles police force, he aggravates not only the police, but Mary Strand, the head of his studio's publicity department, as well. Bill's screen "super sleuth" persona suddenly takes on reality when he receives a death threat from the "Poison Pen," an at-large celebrity killer who wants to murder Bill in retaliation for his last bad movie. After being shot at through the window of a Hollywood nightclub, a cocky, determined Bill goes with Mary, who secretly loves the dumb star, to see amateur criminologist and house-of-horrors owner Professor Herman, not realizing that Herman is, in fact, the Poison Pen. The next day, Herman shows up at Bill's movie shoot and, during a chase scene, accidentally kills Bill's co-star, Ralph Waring. Because Waring had fought earlier with his stand-in, Larry Frank, Larry is arrested for the crime. Convinced of Larry's innocence, Bill continues his confused efforts to find the Poison Pen, while Herman continues his poorly aimed murder attempts on Bill. Finally, Mary, to protect Bill from himself, tricks him into getting arrested and jailed. Bill "outsmarts" her, however, by calling Herman to bail him out. When Mary deduces that Herman is the Poison Pen, she and Warts, Bill's servant, notify the police and rush to Herman's "Crime Doesn't Pay" horror gallery, where, aided by Herman's clumsiness, they rescue Bill and catch the Poison Pen.