From the game box:
You are Jackie Estacado, a hitman for the Franchetti crime family. On your 21st birthday, a timeless force known as The Darkness awakens within you. You can wreak havoc on your enemies with the powers it bestows. But you'll quickly learn that The Darkness has a will of its own...
User Summary
On the evening of Jackie Estacado 21st birthday, Jackie is targeted for assassination by his "Uncle" Paulie Franchetti out of sheer paranoia that Jackie is after his position as the Don. As night falls, the Darkness (Mike Patton) - an ancient demonic force which has inhabited Jackie's bloodline for generations - violently manifests and massacres his pursuers. With his new powers, Jackie gradually dismantles Paulie's drug and money laundering operations.
The game includes a range of modern-day weapons as well as the powers of the Darkness, which include summoning four imp-like creatures called "Darklings" that can attack foes, using "Dark" tentacles to impale foes or break down walls, using "Creeping Dark" tendrils that sneak along floors, walls and ceilings to take out foes from a distance, and creating a black hole that sucks anything nearby into it. The Darkness powers cannot be used in a well-lit area but can be used in darker areas and under total darkness; the player is able to shoot out lights to help increase the amount of dark energy available. Additionally, by letting the Darkness consume the hearts of its victims, the player can further increase the effects of the Darkness powers.