As the 31st Marine Expeditionary Unit prepares to deploy in the Pacific, they kick off grueling tests of combat readiness — and failure isn't an option.

While transporting the 31st MEU, Navy vessels encounter a foreign spy ship. Later, the Marines continue CERTEX to test their skill, unity and resolve.

As the Scout Sniper platoon faces an uncertain future, the 31st MEU carries out its most demanding exercise yet: a beach raid under cover of darkness.

The USS America and USS Green Bay head to port — until global events demand a sudden change in mission. At home, several Marines consider what's ahead.