Based on the screenplay The Captain's Paradise by Alec Coppel
Changing locales from the film that provided the source material, Oh, Captain! tells the story of Captain Henry St. James, captain of a ship that travels between London and Paris. The Captain keeps a home in a London suburb and one in Paris, each supplied with a wife, neither of whom knows, of coruse, about the captain's other wife. The ship's schedule gives the Captain a weekend in one city, five days at sea, followed by a weekend in the other city, and so on.
Maud, his English wife is the very model of English reserve and decorum, the perfect wife for an English gentleman. His Paris wife is Bobo, a nightclub singer with a notably voluptuous figure who longs for the quiet domestic life that the Captain has imposed on the restless Maud.
The Captain's first mate, Manzoni, envies him for his two contrasting wives but worries that this cannot end well for the parties involved.
While the captain is away, Maud wins a recipe contest. To celebrate, she decides to fly to Paris for a bit of fun and sighseeing and to surprise her husband. Meeting an amorous Spaniard on a tour bus, she surprises him by seeming more open to his advances than he expected. Maud and the Spaniard go out on the town, turning up at the nightclub where Bobo performs.
The Captain arrives and is furious to see his wife flirting with another man. The wives meet and their anger at each other soon dissipates as they realize they've each been equally deceived by Henry.
Bobo, completely tired of leading a life that makes her unhappy, goes off with Manzoni. Henry pleads with Maud to stay with him, but she leaves. Henry blesses the union of Bobo and Manzoni by giving them the ship. At the finale, Maud returns to Henry.