The Navajo Trail (movie, 1945)

U.S. Marshals Nevada Jack McKenzie and Sandy Hopkins are working undercover to capture a gang stealing horses from the Navajos, and to capture the killer of a Ranger. Nevada poses as an outlaw to get in with the gang and find the leader, while Sandy pretends to be a drunken old horse thief that has knowledge of where the Navajos have hidden their ponies.