A Spanish spy and an American heiress battle fascists in England.

Denard, a former musician now working for the Loyalist side in the Spanish Civil War, travels to England with a letter of credit to buy a large amount of coal from the British in order to keep it out of the hands of the fascist rebels. Upon landing in England, Denard is detained in customs and misses his train. Rose Cullin, the daughter of Lord Benditch, a coal tycoon, has also missed the train and offers Denard a lift in her rented car. When the car has a flat tire, Rose suggests that they stop at a restaurant and have a meal while the tire is being repaired. Licata, the fascist agent, has also stopped at the restaurant and offers to buy Denard's letter of credit. Denard, whose wife and daughter were murdered by the fascists, rejects his offer. Unable to persuade Rose to leave the roadhouse, Denard takes the car, but is stopped on the road by Licata, his chauffeur, Rose and Captain Currie, a British fascist sympathizer. The chauffeur beats Denard, and while he is unconscious, Licata searches his wallet but does not find the letter which Denard earlier hid in his shoe. Completing his journey on foot, Denard arrives at a hotel owned by his countrywoman Mrs. Melandez. Rose calls him there and asks him to meet her so that she can apologize. In the meantime, Denard meets Contreras, his contact, at a language school. Afterward, on his way to meet Rose, Denard is ambushed. Denard accuses Rose of setting him up, but she reveals that Currie also knew they were planning to meet. Denard then tells Rose why he is in England, and she advises him on the best way to approach her father with his request. At the hotel, Else, the young maid, warns Denard that Melandez and Contreras have searched his room and are waiting for him. Melandez first accuses Denard of selling his letter of credit to Licata, then shows him a letter relieving him of his assignment. Denard does not trust Melandez, however, and announces that he will complete his mission. He asks Else to keep the letter of credit during the night and the next morning tells Melandez that he plans to take the girl with him after his work is finished. Later, when Melandez is ordered to make trouble for Denard, she kills Else by pushing her out the window. Before Denard can complete his deal with Lord Benditch, his letter of credit is stolen, and he is arrested for Else's murder. Denard pulls a gun and escapes, determined to avenge the dead girl. At the hotel, he overhears Mr. Muckerji, another tenant, tell Melandez that he has informed the police that a witness saw her murder Else. Melandez then poisons herself. Although Denard is now unable to buy coal to keep it from the enemy, he decides to try to stop the miners from re-opening the closed mines. He makes an impassioned speech, telling the miners that the coal will be used to make munitions in Spain, but the men are more interested in jobs than in politics until a miner whose son is fighting in Spain speaks on behalf of the Loyalists. One of Licata's men shoots at Denard, and in the ensuing confusion, Rose helps Denard escape. She asks her father's friend, Forbes, who wants to marry her, to help Denard leave the country. Before he returns to Spain, Denard learns that the contract between the mine owners and the fascists has been canceled. When he boards the ship that will take him home, Denard finds Rose waiting for him.