H. J. Mavity, painter of paperback romance covers, has a perplexing riddle to solve when her ex-boyfriend, Rick Dell, collapses at her feet after telling her that the words "ninety-nine clop clop" hold the clue to a lot of money. Although Dell has clearly been murdered, H. J.'s avarice gets the better of her and she determines to risk the ire of whoever has killed Dell to go after the money. First, however, she must understand the riddle and who better to help her than her ex-husband, Ben Spanner, a gifted mimic whose voice is known to millions through TV and radio commercials. Ben knows just about every show business joke around and will surely be familiar with the routine of a hack stand-up comic like Dell. Ben is some¬what aggrieved to see H. J. again for he knows better than anyone else that she spells trouble. He comes through with the riddle to which "ninety-nine clop clop" is the solution but H. J.'s lingering attraction for him overcomes his common sense and he, too,is soon in pursuit of the stash Dell's clue points to—though more to protect H. J. than to feather his own nest.

Little does Ben suspect that H. J. has plans that don't include him. When a new job takes him to New York City to play the voice of an English muffin, H. J. takes the opportunity to slip away from his Connecticut home with the contents of Dell's hideaway. Ben, who thought he had convinced H. J. that their and should be turned over to the police, must now use all his ingenuity to save her from a desperate killer.