The story follows a group of sailors aboard the British freighter SS Glencairn, navigating the treacherous waters of the North Atlantic during World War II. As they travel from the Caribbean to England with a cargo of explosive materials, the crew faces a series of perilous challenges, both from the external threat of enemy submarines and the internal tensions among themselves. The captain and the sailors, hailing from various backgrounds, struggle with their own personal issues and forge fragile relationships amidst the ever-present danger. Their camaraderie is tested as they contend with the harsh realities of war and the isolation of life at sea.

Olsen, a naive and earnest Swedish sailor, dreams of returning home to his family's farm. His shipmates, including Driscoll, a warm-hearted Irishman with a fondness for drink, and Smitty, a mysterious man keeping to himself, each bring their unique hopes and burdens to the collective environment. The interactions between them reveal deep-seated fears and hidden loyalties, as they cope with the loss of crew members and mounting suspicions in an environment where trust is as valuable as survival. Early challenges lay bare personal vulnerabilities, leading to conflicts and poignant moments of understanding. As danger looms ever closer, the men must confront their own demons before facing the external threats that jeopardize their mission and their lives.