Lee Thomas was a British Intelligence officer. Along with Olaf Christiansen and Edward Carraciola, he was a Nazi spy. The three, along with Torrance-Smythe and George Harrod, were selected as part of Major Smith's commando team to rescue General Carnaby from the Schloss Adler before he could reveal details about the Allies' second front. At least, this is what they and their superior, fellow Nazi spy Wyatt-Turner, were told. During the mission, the three murdered Torrance-Smythe and Harrod and did all they could to ruin Smith's plans.
After being captured in the Zum Wilden Hirsch by Colonel Weissner and his men, Thomas was taken to the Schloss Adler. There, he, Christiansen and Carraciola revealed themselves as German spies to commanding officer Paul Kramer, and were welcomed as guests of honor at dinner in the Golden Hall, in an attempt to demoralize the stubborn Carnaby.
However, Smith appeared with Morris Schaffer, and convinced Kramer that "Thomas" was an impostor. He insisted the real Thomas, Christiansen and Carraciola had been arrested and replaced with fakes to trick the Nazis. Told the only way they could prove themselves was to write down the names of all their fellow spies back in Britain, the trio obliged, only to then realize this was Smith's plan all along! Furthermore, "Carnaby" was actually actor Cartwright Jones, and the rescue mission just an excuse to get the three suspected traitors into a situation where they'd reveal the identities of all their fellow agents in Britain.
The three were taken prisoner after Kramer and the other Schloss Adler Nazis were incapacitated. During the escape from the castle, Thomas feigned a hurt ankle. When Schaffer stopped to help him, this allowed Christiansen and Carraciola to grab the American and take him hostage. They demanded Smith let them go, or else they'd kill Schaffer. When Smith agreed, Thomas and his comrades released Schaffer, boarded a cable car, and left. Smith jumped onto the roof and planted a bomb. Carraciola climbed up to try and stop him, but was knocked off. Further efforts to dislodge Smith failed, resulting only in Christiansen being injured.
As another cable car passed them, Smith jumped onto it. The bomb severely damaged the one containing the two traitors. Christiansen slid out the open door. When the car came loose from the track and fell, Thomas made a desperate leap and managed to grab the cable above, but he couldn't hold on. Losing his grip, he fell thousands of feet to his death.
- In the film, Thomas is killed by an SS officer before the group gets to the cable cars. When the group is trapped in the radio room, Smith forces him at gunpoint to climb out the window and down a rope, while he and the others hide in a closet. When the SS burst in, the officer in charge sees the rope, and, leaning out, shoots Thomas. Thomas is killed and plummets down the side of the castle. The role of the final spy aboard the cable car is taken instead by Ted Berkeley, the film's version of Edward Carraciola.
- Thomas has a British Army captain's rank insignia in the film. His rank isn't given in the novel.
- Some sources for the film identify him as "Philip Thomas."