Dr. Howard Bannister, a musicologist from the Iowa Conservatory of Music in Ames, Iowa, travels to San Francisco to compete for a research grant offered by Frederick Larrabee. Howard is accompanied by his tightly wound, overbearing fiancée Eunice Burns. The pair checks into the elegant Hotel Bristol, where fate quickly twists around them as Howard crosses paths with the charming trouble-magnet Judy Maxwell in the hotel’s drugstore. Judy, who never finished college but has soaked up a surprising breadth of knowledge from the many schools that expelled her, quietly starts to pursue Howard and even finds a way to lodge herself in the hotel without paying.
Howard arrives with a plaid overnight bag filled with igneous “tambula” rocks that possess peculiar musical properties, utterly unaware that three other parties sharing the same floor on the Bristol also carry identical bags. The negotiation of these bags’ contents soon spirals into confusion: a mysterious "Mr. Smith" has a bag with top-secret government papers, and government agent "Mr. Jones" is on a mission to recover them; wealthy socialite Mrs. Van Hoskins guards a bag full of precious jewels; Judy’s bag contains clothing and a hefty dictionary; and Judy herself is increasingly entangled in Howard’s life. As the night unfolds, the four groups—unwittingly and disorientingly—swap bags, mixing up identities and intentions in a comedy of near-misses and mistaken loyalties.
The tension peaks at the musicologists’ banquet, where Judy, masquerading as Eunice, uses wit and studious flair to win over most of the crowd, much to the chagrin of Howard’s Croatian competitor Hugh Simon. Howard, suspicious of Judy’s ruse and eager to protect his chance at the grant, denies knowing the real Eunice when she tries to enter the banquet. The deception intensifies when Judy slips into Howard’s hotel room, and the pressure to keep her presence hidden amid the thieves’ pursuit leads to a wild fire and the destruction of the room. By the end of the ordeal, the jewels remain with Judy, the government papers with Mr. Smith, Judy’s clothes with Mr. Smith, and the rocks with the thieves, while Howard and Eunice each hold fragments of the night’s tangled fate.
The following day brings a grand reception at Larrabee’s upscale Victorian home, where a chaotic clash erupts—guns, furnishings, and pies flying in every direction. Howard and Judy manage to reclaim all four bags and flee, first on a delivery bike and then in a wedding-party-decorated Volkswagen Beetle, with [Mr. Smith], [Mr. Jones], and the jewel thieves in hot pursuit. The chase spirals through Chinatown during a parade, winds down Lombard Street, punches through a glass panel, wades through wet cement, and finally ends with a splash into the San Francisco Bay at the ferry landing. The pursuit drags on into a courtroom, where Judge Maxwell is barely keeping it together as he tries to sort out the mess, and his nervous system is further taxed by the revelation that it is his own daughter, Judy, who has caused much of the trouble. After the dust settles, the bags are returned to their rightful owners, and the tangled crew scatters into a fragile new arrangement.
At the airport, Howard and Judy reunite amid the aftermath: Eunice appears with Larrabee and Simon, who have won the grant, but Judy exposes Larrabee as a plagiarist, clearing the way for Howard to receive the grant in the end. Eunice leaves Howard for Larrabee, opening a new chapter of the story. Howard boards a plane back to Iowa, only to discover Judy waiting in the seat behind him. He confesses his love and apologizes for the earlier harsh words. She retorts with a playful wink to cinema history: > Love means never having to say you're sorry. <br>
As the plane’s screen fades to credits, a clip from the Looney Tunes cartoon What's Up, Doc? plays, leaving the duo in a moment of shared affection and comic bliss.
