At Greenglass House, a smuggler's inn, twelve-year-old Milo, the innkeepers' adopted son, plans to spend his winter holidays relaxing but soon guests are arriving with strange stories about the house sending Milo and Meddy, the cook's daughter, on an adventure.

"Fresh off the excitement of the Night Hunt, Ruskin, Cinder, Groth, and Roke set out for a camping trip on Ghost Island, which, according to Groth, is definitely not haunted--despite its name"--