In 1941, Henry Bremmer [Frank Reicher], a German-born owner of the Park Hotel in New York City, faces the rapid onset of World War II tensions. As the United States prepares for possible conflict, Bremmer nervously anticipates Germany’s declaration of war following Japan’s attack on Pearl Harbor. His wife is currently in Germany recuperating from surgery, and he enlists his lawyer, Carl Becker [Craig Stevens], to help arrange her safe passage to the U.S. However, both the State Department and the German Embassy are unable to provide assistance, adding to Bremmer’s anxiety.
Bremmer’s chauffeur, seeking a way to help, suggests reaching out to Dr. Woodford [Robert Warwick], a man with supposed contacts in Germany. Unknown to Bremmer, Dr. Woodford is actually the mastermind behind a Nazi spy ring operating covertly at the hotel. The hotel staff, including the chauffeur, are part of this dangerous conspiracy. Vice to his efforts, Woodford blackmails Bremmer’s wife into cooperating and promises to get her to safety in the U.S. if Bremmer complies.
Meanwhile, Carl Becker considers enlisting in the military but becomes involved in counter-espionage efforts when he visits his friend Jim Jackson [Charles Lang], who is in town and also involved in investigations about the spy ring. During their meeting, Carl also mentions his girlfriend, Paula Fengler [Faye Emerson], a lounge singer performing at the hotel. Jim, who is eager to assist and also works with John Trent [John Ridgely], agrees to stay in the hotel temporarily, unaware that the spies have recognized Jim from a photograph and are preparing to eliminate him.
The situation escalates quickly when Jim checks into the hotel. The spies realize who he is and demand Bremmer disclose his identity. In a ruthless act, Dr. Woodford orders Jim's assassination. A bellhop delivers a radio device to Jim, which activates and releases poison gas, leading to his presumed suicide. The police declare Jim’s death as a suicide, but [Carl] does not believe this explanation.
Distrustful of official reports, Carl travels to Washington to join Counter-Espionage. Initially, John Trent suspects Carl might be part of the spy ring, but he soon comes to trust him. As more agents are mysteriously killed, Carl and John return to New York to intensify their investigation. Paula becomes involved romantically with Carl, and he confesses his new role, to which she responds, "I'm glad you're not after me." Carl, in a charming reply, says, "What makes you think I’m not?" Only to warn her later when she calls Woodford to alert him, risking everything as Woodford secretly eavesdrops.
Woodford orders Bremmer to retreat to a hunting lodge in the Adirondacks, where the spy ring’s operation is still active. During their stay, Carl and John ambush the spies at the lodge, capturing Woodford and other agents. However, they are soon attacked on a train heading to Washington, when Nazi operatives free the remaining spies in dramatic fashion.
Following a crucial clue left by Bremmer, the agents locate the spy cell at the Adirondack lodge, where the Nazis are using Bremmer’s ham radio to communicate with a German submarine. Bremmer’s quick thinking involves setting a trap with the same radio, which leads to a fierce gunbattle, during which Bremmer is fatally shot. With the help of tear gas and police, all the spies are captured, except for Woodford, who manages to escape.
In the final moments, Woodford returns to the hotel to retrieve his wife, Paula. Carl arrives just in time, confronting Woodford. When Woodford pulls a gun, Carl acts swiftly and shoots him with his concealed weapon. With the threat neutralized, Carl informs Paula that he is taking her away on a "little trip," but in reality, he arrests her, revealing that she was part of the spy ring all along.
This tense tale of espionage, loyalty, and deception showcases the dangerous clandestine operations happening in America during the early years of WWII, with heroism and betrayal intertwined at every turn.
