Mysterious gateways and glowing spheres of electromagnetic power have begun appearing in the oceans all around the globe. The gateways, which come to be known as Thresholds, are believed to be the key to ultimate power for whoever can solve their mysteries. Numerous forces from around the world struggle to take control of the Thresholds, including the CIA, former Soviet leaders, eco-terrorists and an apocalypse cult.
The game essentially plays like an underwater version of Twisted Metal, with one central twist: the ultimate goal of each level is not to wipe out your enemies, but to collect all five pods in the level and make it to the Threshold with them. Each pod bestows your sub with a different enhancement, such as extra health or higher weapon damage. The catch is that the more pods you're carrying, the more you'll be targeted by your enemies; getting to the exit with all five can be a difficult task. Multiplayer modes include a Battle mode that plays like the single-player story as well as a straight-forward deathmatch mode.