The game is part first-person shooter, horror flick, and morality tale. Players explore a failed underwater utopia torn apart by clashes over a DNA-altering substance that bestows health and superpowers.
Players have to collect the substance in order to gain more abilities and advance through the game.
The catch is that the only source is "Little Sisters", small girls who are guarded by "Big Daddies", lumbering fellows in deep-sea diving suits whose skin-crawling bellows sound like angry whales.
Players can either kill the girl to harvest the substance, or rescue them for a lesser amount and the promise of rewards later, a choice that heightens the game's disturbing atmosphere and affects the story later on.