We open in the bar of a fashionable New York hotel. Business magnate Elisha J. Whitney enters and reveals to the bartender that before sailing that evening to close a big business deal in London, he needs a strong drink to muster the courage to fire his office manager, Billy Crocker. The ever-cheerful Billy arrives and informs Whitney that he’s bound to have a great time aboard ship, because the evangelist-turned-nightclub singer Reno Sweeny and her Angels are also passengers. Despite their friendship, Whitney fires young Billy. Reno enters, and Billy introduces her to his now-former employer. Reno, who has a crush on Billy, suggests to Whitney that he bring Billy along on the voyage. Embarrassed, Whitney excuses himself. Billy explains what a great time Reno will have in London, but she comments that it makes a difference that he won’t be there (“I Get a Kick Out of You”). Billy tells her that he’ll go down to the ship to see her off, and after she leaves, confides in the bartender that he and Reno are “just playmates”, and that he has met another girl.

We meet the passengers as they board the ship (“Bon Voyage”), their departure covered by a reporter and photographer for the ‘Society’ page of the paper – unfortunately, the only celebrity on board appears to be Reno. Other passengers photographed include Sir Evelyn Oakleigh (a rich English Gentleman), Hope Harcourt (American debutante and Evelyn's fiancée), Mrs. Wadsworth Harcourt (Hope's mother), Bishop Henry Dobson (a minister), and Ching and Ling (two of Bishop Dobson's Chinese converts). Billy, who is looking for Reno, bumps into Whitney, who is touched to think his former employee has come to see him off. Whitney suddenly remembers that, in his haste to leave the office, he has forgotten to get a signature on a contract and thus can be left out of the very deal that is taking him abroad. Whitney swiftly rehires Billy, who vows to race back to the Waldorf to obtain the signature. Two federal detectives come on board, looking for “a couple of muggs trying to make a getaway” –one dressed as a preacher. Enter Moon Face Martin, dressed as a clergyman (The Reverend Doctor Moon), Bonnie, the moll of notorious gangster Snake Eyes Johnson – Public Enemy Number One. Searching for Snake Eyes, who’s supposed to join them on board, they encounter Bishop Dodson, who mistakes Moon for the real thing – just before the federal men drag the Bishop off the ship in the show’s first (of many) cases of mistaken identity.

Billy is about to debark to get that signature, when a girl appears – his true love, Hope Harcourt, en route to London to marry Lord Evelyn. Billy suggests that she leave the ship with him immediately and get married, she rebuffs him. Billy is torn – does he leave the ship and get that signature, saving his job, or does he stay on board to try and convince his love that she’s making a terrible mistake? He decides to stay, but lacks a ticket and passport. Moon, having taken a fancy to Billy, offers him Snake Eyes Johnson’s ticket and stateroom berth, as his fellow gangster was “detained” before reaching the ship.

On the upper deck, Hope and Evelyn are walking in the moonlight, but Hope is the only one enjoying it. Billy appears and encourages Evelyn’s notion that he is sea-sick, which sends the Englishman to his cabin to retire. Hope explains that her impending marriage is a marriage of convenience for the financial well-being of her family – but it’s apparent that she prefers Billy (“All Through the Night”).

The next morning, Billy returns from his romantic night on deck with Hope. He must change clothes, but has no luggage. Moon steals Whitney’s shoes and, because Billy must hide from his nearsighted boss, Whitney’s eyeglasses. Billy hides in Whitney’s cabin when the purser arrives with a bucket of ice.