The waterfront pub is closing up and the sailors are staggering home. World War II means a blackout in the English port town of Werrymouth, but the locals have no trouble finding their way over the Halfpenny Bridge, where a small toll shaves a mile off their drunken walk. A group of them are about to cross when a ship comes into the channel, and the lighthouse snaps on to guide its way. As the beams rake across the harbor, the sailors see two men struggling by the shore. One overpowers the other, killing him in the surf.
The murderer escapes, and Detective-Inspector Littlejohn ventures down from London to find him. Two more murders follow, bringing this center of shipping to a halt just when England needs it most.