It's Christmastime, and the precocious Flavia de Luce - an eleven-year-old sleuth with a passion for chemistry and a penchant for crime-solving - is tucked away in her laboratory, whipping up a concoction to ensnare Saint Nick. But she is soon distracted when a film crew arrives at Buckshaw, the de Luces' decaying English estate, to shoot a movie starring the famed Phyllis Wyvern.

Amid a raging blizzard, the entire village of Bishop's Lacey gathers at Buckshaw to watch Wyvern perform, yet nobody is prepared for the evening's shocking conclusion: a body found, past midnight, strangled to death with a length of film. But who among the assembled guests would stage such a chilling scene? As the storm worsens and the list of suspects grows, Flavia must use every ounce of sly wit at her disposal to ferret out a killer hidden in plain sight.