In the late 1800s, in New England, Abigail Rook and her employer, private detective R. F. Jackaby, are the people to call when paranormal phenomenon occurs. When the owner of a species of shape-shifters disguised at kittens is found murdered and an unidentified beast begins attacking people and animals in a nearby town, Rook and Jackaby find themselves on the trial of a monster, a thief, and a murderer.