Daniel Garner was an ordinary man until the stormy night when he and his wife Catherine headed into town to celebrate her birthday. Despite the rainy conditions, Daniel took his eyes off the road to gaze at his wife, and ended up in a head-on collision with a cube van. Both Garners were killed instantly, and while the pure and noble Catherine ascended to Heaven, Daniel found himself neither worthy of eternal bliss nor deserving unending damnation in Hell. He found himself trapped in Purgatory, where he spent thirty years obediently serving the forces of good, as embodied by Sammael, an angel and messenger from God, in the hopes that he could redeem the actions that left him stuck in neutral territory and be reunited with his wife.
As Painkiller begins, he is given one final task: Kill four of Lucifer's top lieutenants, whose demonic armies are slowly encroaching upon Purgatory, with the ultimate goal of turning the supposedly neutral ground into a second stronghold for the forces of evil, hoping to use the advantage to invade and destroy Heaven in turn. If Daniel kills these lieutenants, the invasion will be stopped, and he will be forgiven his sins and allowed to be with Catherine again.