On leave in Naples, a group of Royal Navy sailors visits their old friend, Knocker White Richard Attenborough, a baker who is proudly showing off his huge brood—twelve daughters and, to his great relief, a newborn son. To allow one of the daughters to go out that evening, the sailors are asked to bring the infant along to an outdoor dance, a ritual that sets the stage for a night of mischief and camaraderie.
Puncher Roberts [John Mills] is well known among the crew for his propensity to fight and drink, and despite his best efforts to reform, he still finds himself provoked by two sailors from another ship. The tension erupts while Knocker is dancing with the eldest daughter, and a brawl spills into the square. In the confusion, Puncher is knocked unconscious, Knocker and the elder sister vanish as police arrive, and the baby is left behind in the square.
When Puncher comes to, he discovers the square is empty except for the lonely infant. With no sign of Knocker or the baby's eldest sister, he makes a bold move: he smuggles the baby aboard their ship, leaving a chalk message on the wharfside to tell Knocker that he has taken 'Number 13' on board. From then on, he enlists the help of his fellow sailors to care for the child while keeping it hidden from their superiors, all within the broader framework of ongoing joint operations with Allied navies off the Italian coast.
Knocker seeks assistance from his more casual shore-based senior officer, but finds little traction as the ship maintains radio silence. The sailors, meanwhile, grow closer to the baby’s unexpected presence among them, and the baker’s extended family becomes a source of warmth and tension as the delay in returning the infant stretches into days.
Back on the home front, the Captain faces a potential setback during a training exercise and confronts a choice that could expose the unit to embarrassment. He leverages the baby’s presence to avert a humiliating loss, turning an awkward situation into a chance to demonstrate resolve and teamwork. Through it all, the infant remains a quiet force that binds the crew, the baker’s clan, and the ship’s hierarchy together.
As the mission rolls onward and the ships sail under the shadow of the war’s demands, the original bond between Knocker, Puncher, and the baker’s family endures. When the moment finally comes for the ships to return to port, the long-awaited reunion unfolds not just in the hold of the vessel but in the eyes of a family that has learned to endure separation, uncertainty, and danger with patience, humor, and steadfast loyalty. The voyage ends with a warm, hopeful convergence on board, where the entire family is joyfully reunited and the crew finds a sense of home amid the vastness of the sea.
