Karen White can open 'doors' between universes. This power, which she shares with her brother and sister, has been suppressed since childhood. But now it appears in her teenage son, Michael, who is approached by a mysterious figure known only as the Grey Man, a figure who has haunted Karen's dreams for decades.

Fleeing to her sister Laura's reality, Karen and Michael undertake a terrifying and painful journey into the past, to discover the secret of their power - and the truth about the Grey Man and his masters.