The 101st Cavalry discover the survivors of an Apache raid on a wagon train: a young boy, Rusty, and his dog, the German shepherd 'Rin Tin Tin'. Both are both brought back to 'Fort Apache' where they are unofficially adopted by lieutenant Ripley 'Rip' Masters. Together Rusty and 'Rin Tin Tin' face one adventure after another as they help the cavalry subdue the Apache uprisings and try to maintain law and order.