Ryan Lennox is technically dead but still he remains on earth and works for the heavenly organization EtherLight. But also Ryan does a pretty good job, his boss doesn't approve of his not-so-heavenly-methods. So he fires him and puts an assassin on his tail. After the failed murder-attempt, Lennox gets hired by Lazarus, boss of the Abyss - the natural enemy of EtherLight. EtherLight had killed all of his agents and now prepares the final blow to get rid of Abyss once and for all. Ryan now, under the guidance of Black, needs to prevent this from happening.
Black gives Ryan for that task a few powers like teleportation, telekinesis or a way to make his shots more powerful. But those actions require mana and since Lennox is now a creature of the dark and evil, he needs either to stay in the shadows or convict sins (like killing the EtherLight agents) in order for his mana to regenerate. If he comes near holy places like churches or rooms full of light, his mana decreases and he can only rely on his conventional weapons which range from pistols over machine guns to a full-grown rocket launcher. To get ammunition, security cards or to replenish his life-energy, Ryan has to suck out the remains of the enemies he just killed for those things.