A man calling himself Henry Faber (Donald Sutherland) is actually a German spy nicknamed “the Needle” because of his preferred method of assassination, the stiletto. Cold and calculating, he is emotionlessly focused on the task at hand, whether the task is to signal a U-boat or to kill anyone who poses a threat to his mission.
In England, he obtains critical information on the Allies’ plans for the Invasion of Normandy but is unable to transmit the information. After narrowly escaping British intelligence in London, Faber tries to make his way to Nazi Germany, but he is stranded by fierce weather on Storm Island, which is occupied by only a woman, Lucy (Kate Nelligan); her disabled husband, David (Christopher Cazenove); their son; and a shepherd, Tom (Alex McCrindle).
A romance develops between the woman and the spy, largely because of an estrangement between Lucy and her husband, an accident on their honeymoon having rendered him embittered and physically confined to a wheelchair.
David has always been suspicious of Faber and, having discovered the mysterious guest is carrying military information, demands an explanation from him at gunpoint. A struggle ensues, which ends with Faber throwing David off a cliff.
Lucy, chancing upon her husband’s dead body, realizes that Faber has been lying to her, and she hatches a plan to get away from him. However, her flight alerts him that she is suspicious, and he pursues her. Lucy, after discovering Tom’s dead body, radios the mainland. She is told that help will be sent immediately, but in the meantime, it is vital for her to destroy the island’s radio transmitter.
She is confused by the request, but before she can do anything, Faber appears and threatens to kill her son if she does not do as he says. The Needle tries to use the radio to report to his superiors the exact location of the D-Day invasion, but just as he is about to impart the information, Lucy, having heard him speaking in German, blows the house’s fuses, rendering the transmitter useless.
Faber expresses admiration for what Lucy has done and tells her that the war has come down to both of them. Thinking Lucy poses no further threat to him, he heads towards the shore to be picked up by a German U-boat, as previously arranged.
Lucy, now fully aware of the stakes that are involved, chases Faber to the sea and shoots wildly at him with her husband’s pistol as he tries to launch a small rowboat to reach the U-boat that lies just offshore. One of her shots strikes Faber but does not instantly kill him, and as he struggles to launch the boat, he falls forward dead.
Having been unable to transmit his information or reach the U-boat to get away safely, his mission has been thwarted. Soon afterward, the British intelligence agent who was chasing Faber arrives with the police. He encounters a despondent Lucy, Faber’s body, and the fleeing German submarine.