Boxing Day circa 1935. A Christmas party in a snowed-in manor on the edge of Dartmoor, England. Overhead, in the attic, lies the dead body of Raymond Gentry, gossip columnist and blackmailer. But the attic door is locked from the inside, its sole window is traversed by thick iron bars and, naturally, there is no sign of a murderer or a murder weapon.

Despite the snowdrifts, the local doctor manages to fetch Trubshawe, a retired Scotland Yard inspector, from his cottage a few miles away. Trubshawe politely questions all, or nearly all, of the suspects and finds a lot of skeletons in a lot of cupboards, but it is one of the house guests, the formidable Evadne Mount, best-selling author of countless classic whodunits, who discovers the solution. In fact, were she not its presiding sleuth, The Act of Roger Murgatroyd is exactly the type of whodunit she herself might have written…