Medical hilarity on the high seas as Dr. Simon Sparrow (Dirk Bogarde) takes to the waves to escape the boredom and monotony of a GP's practice ashore. His plan succeeds but not quite in the way he had expected when he joins the crew of a cargo ship bound for the tropics.

Sparrow signs up as a medical officer onboard the cargo ship SS Lotus, pleased to be free of any female distractions. However, Sparrow soon falls foul of the ship's skipper, fearsome captain Hogg (James Robertson Justice) and worse still, lands in jail after a drunken celebration on arrival in South America. Two new passengers, Muriel (Brenda de Banzie), the daughter of the shipping-line owner, and Helene (Brigitte Bardot), a beautiful French singer, come aboard to pursue the Captain and Simon romantically.

It's full steam ahead for fun, sunshine, love and adventure in a comedy cruise with a doctor who is most definitely all at sea!