In 1892, New Fiddleham, New England, things are never quite what they seem, especially when Abigail Rook and her eccentric employer, R. F. Jackaby, are called upon to investigate the supernatural.
First, members of a particularly vicious species of shape-shifters disguise themselves as a litter of kittens. A day later, their owner is found murdered, with a single mysterious puncture wound to her neck. Then, in nearby Gad’s Valley, dinosaur bones from a recent dig go missing, and an unidentifiable beast attacks animals and people, leaving their mangled bodies behind. Policeman Charlie Cane, exiled from New Fiddleham to the valley, calls on Abigail for help, and soon Abigail and Jackaby are on the hunt for a thief, a monster, and a murderer.