The fourth in Pulver's series featuring cantankerous detective Peter Brichter and his heiress-wife/horse-lover Kori pays homage to the sequestered house-party genre. Here, Kori invites her only living relative, Cousin Evelyn, to join her--as well as Peter, the baby, the new nanny, the stableboy, Kori's mentor/cook, and a retired police chum and his wife--for a Christmas party at Tretower, but Evelyn has barely settled in before, somehow, she's bopped on the head and dies--and then a blizzard cuts the house off from help. Whodunit and why? The answers involve a secret passage, a reexamination of Kori's family tree, and the (supposedly willful) years-ago disappearance of drab Evelyn's pretty sister Inez. Clever trickery in the John Dickson Carr classic locked-room puzzle-mode, and, for once, Peter's churlishness and Kori's saintliness are played down. In all: a clever, cozy read.