Combat!

The Impostor (3x10)

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Hanley must take the place of a G-2 officer on a mission to spy on a German HQ. He is to meet three men for the mission. He discovers that one of them has been killed and although the corpse is dressed in a German Uniform, he is recognized by Kirby as an American G.I. They now suspect that one of the three men is a German disguised as an American G.I.