When Meg witnesses the dying moments of a shapeshifting fox and is given a beautiful and powerful stone, her life changes forever. She is plunged into the dark world of the Skulk, a group of shapeshifting foxes. As she learns about the other groups of shapeshifters that lurk around London – the Rabble, the Horde, the Cluster and the Conspiracy – she becomes aware of a deadly threat against all the shapeshifters. They must put aside all their enmity and hostility and fight together to defeat it.