From publisher blurb:
When a creature dies, its soul passes beyond the realms of the living into unknown planes. However, whether from sheer tenacity, a misapprehension of their true state, or a need to finish some uncompleted business many spirits refuse to make this final journey. Mortals know these itinerant souls as ghosts -- existing in a half-world between corporeal reality and the cold, invisible realm of the dead.
Warlocks forge pacts with these spirits, and can call upon their special nature to phase through solid objects, drain foes of life energy, and torment the living with mind-blasting sounds and images.
This pact features a full listing of powers from Levels 1 through 30, four new Feats exclusive to the pact, a paragon path, and three new magic items.