Intangible — C.A. Gray

Peter Stewart grew up on a unique version of the Arthurian legends taught him by his father, a harebrained quantum physicist who asserts that anything is possible. But Peter disbelieves anything which cannot be scientifically explained, despite a nagging sense that there is more to the world than meets the eye. Lily Portman is an orphan with a secret: she can see creatures that are invisible to everyone else. These creatures control every human being she has ever met to varying degrees... until she meets Peter and his father. When a mysterious stranger stages an accident which nearly costs Peter and Lily their lives, suddenly Lily learns that she is not crazy after all, and Peter discovers the truth of his father's stories… including the existence of Arthur's ancient nemesis, one who calls himself the Shadow Lord, and a prophecy with implications so profound that it will alter not only the course of their lives, but potentially the fate of the world.