It's December in the quiet Swedish town of Kymlinge, and the Hermansson family are gathering to celebrate a big family birthday. But beneath the guise of happy festivities, tensions are running high, and it's not long before the night takes a dark and unexpected turn . . .

Before the weekend is over, two members of the Hermansson family are missing, and it's up to Inspector Barbarotti - a detective who spends as much of his time debating the existence of God as he does solving cases - to determine exactly what happened on that darkest day, and unravel a web of sinister family secrets in the process . . .