Irwin Allen 
The Massacre [EPUB ebook] 

Tony and Doug land in 1876 Montana the day before the Battle of the Little Bighorn. They are captured by Chief Crazy Horse and his companions, and Doug manages to escape with the help of the survivor of a troop of soldiers, Trumpeter Tim Mc Kinnis. Tony does not escape and is taken to the Sioux encampment. There, he demonstrates his honesty and bravery to Chief Sitting Bull, moving him to adopt him. Doug and Tim make their way to the 7th Cavalry for help.