Located 35,000 feet beneath the waves is the world's most secure prison, the Devil's Grave. The place houses the worst criminals of humanity, and is completely inescapable. For the inmates, life is simple and predictable. That is, until a World War Two-era submarine crashes into the complex. Further disrupting the tranquility are the sub's survivors, who have spent decades perfecting a weapon to end a war— which is already over . After the weapon is unleashed, the inmates must attempt the impossible—breaking free from an inescapable prison alive . During their journey, they learn why the facility bears its peculiar name…