On December 8, 1941, the United States declared war on Japan. For the next several years, U.S. forces were fully engaged in battle throughout the Pacific, taking over islands one by one in a slow progression towards mainland Japan.During this brutal campaign, the Japanese were able to break coded military, dramatically slowing U.S. progress.

In 1942, several hundred Navajo Americans were recruited as Marines and trained to use their language as code. Marine Joe Enders is assigned to protect Ben Yahzee - a Navajo code talker, the Marines' new secret weapon. Enders' orders are to protect his code talker, but if Yahzee should fall into enemy hands, he's to "protect the code at all costs." Against the backdrop of the horrific Battle of Saipan, when capture is imminent, Enders is forced to make a decision: if he can't protect his fellow Marine, can he bring himself to kill him to protect the code? The Navajo code was the only one never broken by the Japanese, and is considered to have been key in winning the war.