All of Great Britain is caught in the grip of a ghost epidemic. In the fourth adventure of the ghost-hunting agency Lockwood & Co., Anthony Lockwood and George are faced with a particularly horrific crime. To solve this case, they must mobilize all their resources, and so they ask the exceptionally talented Lucy, who has a gift for dealing with ghosts, to return as a consultant. However, the friends are unaware that their investigations will awaken forces that even they cannot control.