Hercule Poirot's Silent Night by Sophie Hannah

Summoned by a formidable matriarch to spend Christmas at a remote country house, a famed Belgian detective and his Scotland Yard friend are drawn into a discreet inquiry linked to a nearby convalescent home, where a gravely ill patient’s family faces threats and unsettling incidents; amid snowbound isolation, prickly hosts, and conflicting testimonies, they unravel buried grievances and clever misdirection to expose a killer before the holiday turns tragic.

Purchase from Bookshop.org