Heroic German shepherd dog Rin Tin Tin ('Yo ho, Rinty!) and his young orphaned master, Rusty, sole survivors of an 'Injun' raid on a wagon train are found by members of the Fighting Blue Devils of the 101st. Cavalry. Brought back to Fort Apache, Arizona, they are officially adopted by Lieutentant Rip Masters (James L Brown) and made honorary troopers - Rusty is commissioned a corporal and Rin Tin Tin a private.