For the first time in his spectacular career, Spike Tracy, ace detective, was baffled. A woman-Lina Lee-had been shot through the head by an old army revolver in the office of Felix Penton, playboy-publisher. Here, it seemed, was the "perfect crime." There was no lack of evidence. There were too many suspects, too many clues. Not one of those involved had an alibi. And before Spike could even begin to establish a case, there were any number of separate mysteries to be solved, none of which seemed to make sense. What was the meaning of the purple onion in Lina Lee's luxurious apartment? Why were the account books of the Penton Press taken from the safe, and what did the auditor's check-up reveal? Who was the veiled woman appearing so mysteriously at certain crises in Penton's life? And, most important of all, what did a certain newspaper photograph, yellowed with age, have to do with the case? These are only a few of the posers which Spike Tracy encounters as he pursues his investigations. "Murder on Friday" calls for his most brilliant deductive powers. And he comes pretty close to failure when he runs up against the blind devotion which Felix Penton inspires in women....