In 1943, Pat Bannon, the captain of a large Gloucester, Massachusetts fishing boat, The Daniel Webster , is in desperate need of sailors and so hires Conrad, a Dane without identification papers. Pat then reluctantly agrees to take stranger Margaret McLean to Trabo, a village on the Newfoundland coast, where Pat fishes. During the voyage, a small storm hits and fog envelops the boat. Pat hears machine gun fire in the distance and suspects that German U-boats are signaling each other. When sailor Holger, another Dane, shows Pat that the boat's radio has been sabotaged, Pat questions Conrad after Holger reveals that Conrad has refused to speak Danish. The rough-hewn Conrad grudgingly utters some Danish and comments that Holger's Danish is surprisingly polished. Just then, the men hear more gunfire, and Pat realizes that the U-boats are shelling another vessel. Pat and some of his crew, including Holger and Conrad, board the wrecked vessel, which turns out to be a Danish schooner called The Gaunt Woman , and after discovering a dead man up top, locate the ship's dazed, speechless captain, Eric Skalder, down below. Once Pat has inspected the ship's cargo--barrels of costly rum--Skalder finally begins talking, describing how his schooner was blown off course during the storm and his crew abandoned ship after the shelling began. Skalder identifies the dead man as his business partner and states that the Germans planted a bomb on the schooner, which his partner found and deactivated. Skalder offers to pay Pat to tow the schooner, and Pat agrees. That night, while on the deck of The Daniel Webster , Pat notices a light being flashed through a porthole and goes below to investigate. Finding only Margaret awake, Pat questions her. Margaret explains that she is a nurse and is returning to Trabo, her childhood home, to visit her father. When Pat comments that he knows no one in Trabo named McLean, Margaret becomes defensive, claiming that her father, a sea captain who left Trabo many years before, was disabled when his ship was attacked by a U-boat. Later, in the isolated village of Trabo, Skalder accepts Margaret's father's invitation to spend the night at his house, but Pat declines and returns to search the schooner. On board Pat finds Conrad, who states that he became suspicious of Skalder's story because he had noticed bullet holes in a tarp covering a lifeboat, but none in the lifeboat itself, suggesting that the Germans had shot up the tarp while the boat was being used. The two men inspect the cargo area again and there discover a hidden door leading to a large room filled with torpedoes. Now aware of Skalder's true mission, Pat speculates that the schooner was heavily damaged during the storm because it was tied up to a submarine, so Skalder sent his crew away and ordered the shelling to explain the devastation. At that moment, as Pat and Conrad hide, Holger enters the torpedo room to send a coded message over the radio. After Holger leaves, Conrad races to warn the McLeans about the schooner, while Pat greets Skalder, who is re-boarding with his returning crew. A Canadian patrol plane then lands nearby, and the pilot informs Skalder that the schooner will be inspected the next morning. Feigning ignorance, Pat suggests that one of his Danish sailors act as a witness during the inspection, and Skalder selects Holger. Pat hurries to the McLeans', where Margaret reveals that Conrad left his flashlight in the schooner's hold. Sure that the Nazis will destroy the village when they find the flashlight, Pat prepares to shove off that night, while Margaret quietly evacuates the village. All goes as planned until Anderson, one of Skalder's men, shows up at the McLeans' claiming to need a nurse and insisting that Margaret go to the schooner. To protect Margaret, McLean reveals the location of the villagers. Hidden under the McLeans' house, Pat overhears the exchange, and as soon as Anderson leaves with Margaret, he and his crew camouflage some rowboats with gasoline-soaked brush and row out to the schooner. The men set fire to the brush, which ignites the schooner as they are boarding it. A gun battle then ensues, and after all the German crew is subdued and Margaret is rescued, Pat corners Skalder. Skalder insists that a time bomb is set to go off in twenty minutes and is powerful enough to destroy the village. Pat sends Margaret, with whom he has fallen in love, and most of his crew to help move the villagers to a high cliff and instructs Steve, another crew member, to steer the schooner toward the current. Just then, two approaching U-boats are spotted, so Pat decides to blow them up along with the schooner. Skalder, meanwhile, suddenly pulls a gun on Conrad, who is guarding him at gunpoint, and the two men shoot each other. Skalder is killed, but Pat manages to drag the wounded Conrad to a rowboat. Pat, Conrad and Steve row furiously, reaching safety moments before the bomb explodes and destroys the schooner and the submarines.