Gabriel Jordan lives a lonely life on the streets, taking the rare job that usually means spending hours in the cold, waiting for a chance to take a photograph of a cheating spouse. That's how he meets Dr. Aleksei Tennant—who he sees suspiciously jumping from a window of a woman's apartment. Tennant introduces Gabriel to the hidden worlds, magical worlds connected to this one by portals. Gabriel is eager to learn the runes for opening them, Tennant is eager to teach, and a fragile friendship develops amidst a series of murders.