It is Christmas 1890, and Sherlock Holmes and Dr John Watson are visited by a new client.

Eve Allerthorpe - daughter of an eccentric Yorkshire dynasty - believes she is being haunted by a demonic Christmas spirit. Her mother had told her terrifying tales of the sinister Black Thurrick, and Eve is sure that she has seen him from her bedroom window.

What is more, she has begun to receive parcels of birch twigs, Black Thurrick's calling card...