The Legion of Missing Men.

Bob Carter, a member of the Foreign Legion, is glad to see his brother, Don, for the first time in ten years but is sorry that Don has joined the Legion. Bob, Don and Bob's buddies, Muggsy and Bilgey, go to a café and there Don falls for Nina, a singer in love with Bob. Bob doesn't know this and thinks she is Garccia's girl, and warns Don to have nothing to do with her. Don disregards the warning and Garcia discovers Nina and Don together and provokes Don into hitting him. Don is arrested and thrown into the company brig. Nina, with the aid of an Arabian sheik, Ul Ahmed, helps Don escape. Bob, Muggsy and Bilgey follow but are captured and taken to Ul Hamid's headquarters. The sheik tortures Don to force Bob to work some captured machine guns for him. Ah Hamid and his tribe attack the fort, but Bob manages to turn the machine guns against his captors, and the fort is saved.