Jerry Lewis is in zany form here, under the capable control of director Frank Tashlin.
Raised in an orphanage, Lester March (Lewis) is a disaster-prone television repairman, but what he wants most of all is to be a private detective – having devoured all the Mickey Spillane and Dashiell Hammett books he could get his hands on, and bought himself a ‘sleuth kit’. His hero is his friend, seedy private eye Pete Flint (Jesse White).
Finally, Lester gets the chance to assist Flint in tracking down the long-lost heir to a billion dollar fortune left behind by a recently deceased eccentric inventor and electronics tycoon. He proves himself the most bumbling, fumbling detective in the history of law enforcement – mainly because Lester is the heir he himself is looking for.
If the heir cannot be found, the money will go to the tycoon’s sister Cecilia Albright (Mae Questal). Her fiancé, the unscrupulous family lawyer Gregory DeWitt (Zachary Scott), wants the estate all to himself and is shrewdly manipulating events with the assistance of lunatic family butler, Leopold (Jack Weston).
Discovering that Lester is the missing heir to the estate, DeWitt now plans to kill Lester before he can collect his fortune, marry Cecilia and then kill her too and take the fortune for himself.
And so we are treated to the spectacle of Lester searching for himself in a mansion chock full of assassins, cutthroats and murder machines – all working together to place him in an early grave. Worst of all, Lester thinks everybody likes him and is therefore unaware of the plots, sub-plots and counter-plots designed to bump him off (including a hilarious attempt on his life using radio-controlled lawnmowers!).
In spite of all the murderous mayhem, Lester manages to fall in love with luscious nurse, Wanda Paxton (Joan O’Brien).