Zephyr, is deep inside the Moffat Tunnel when the entire Yellowstone Caldera violently erupts, devastating the west. But the passengers and crew of the train are safe inside the 6.2 mile long tunnel. As the ash settles, the survivors must combine all their wisdom, ingenuity, strength, and skill to punch their way out of the mountains and get back to whatever is left of civilization aboard The Last Zephyr.