A young woman named Jennifer Downing is unexpectedly taken while enjoying a relaxing mud bath at a spa. The following day, her concerned father, P.J. Downing, a wealthy shipping magnate, and his glamorous trophy wife, Helen, visit the detective agency, Crumb and Crumb Investigations, in downtown Los Angeles. Eliot Draisen, the agency's president, informs P.J. that he currently has no investigators available for the kidnapping case, but P.J.’s insistence leads him to reluctantly assign the task to Harry Crumb, the clumsy grandson of the agency's founders.
In a comical turn of events, Harry, disguised as an elderly window washer, gets caught up photographing a couple's affair instead of focusing on the case at hand. After a series of mishaps, including a dramatic fall where he swings through a window, Harry is summoned to Los Angeles after realizing he mistakenly followed the wrong subject. Upon his arrival, he impressively recounts the details of Jennifer's case but is quickly reminded that no jewels are involved, as it is merely a kidnapping.
Meanwhile, at the Downing residence, Harry's presence leads to a series of unfortunate incidents where he showcases his utter lack of finesse, like impaling his hand on fishing lures during a meeting with P.J. Additionally, he witnesses Helen flirting with her tennis coach, Vince Barnes, raising Harry's suspicions about her possible involvement in the kidnapping.
Later that evening, P.J. receives a ransom note demanding $10 million. Joining the unfolding chaos is Detective Casey, who is skeptical of Harry's capabilities and suggests an operational strategy. Harry befriends Jennifer’s sister, Nikki Downing, who gives him insight into Helen’s greedy character. Teaming up with Nikki, Harry devises various hilarious and misguided plans to expose the truth.
As the series of comedic events unfolds, Harry’s antics escalate, leading to disastrous consequences that involve his reckless methods of espionage, disguise, and a precarious game of cat-and-mouse with the supposed kidnappers. He discovers that the brakes of P.J.’s car were tampered with, plunging the case deeper into the abyss of convoluted relationships and hidden motives.
In a thrilling finale at the airport, the plot twists when Harry’s accidental heroics reveal the true face behind the kidnapping—the cunning Eliot, who plans to escape to Buenos Aires with Helen after betraying P.J. In a series of misadventures filled with slapstick humor, Harry uncovers Eliot’s scheme and inadvertently foils it, resulting in a showdown that is equal parts comedic and chaotic.
Ultimately, as Jennifer is safely returned, and Harry is appointed the new president of the agency, he reflects on the case with Nikki, who expresses her desire to stay in touch for future investigations. However, just as Harry settles into his new role, he receives a call for another baffling case—a murder in San Francisco—prompting him to transform once again into a whimsical disguise as he leaves his office, setting the stage for more hilarious escapades to come.
