Slight Mourning (The Calleshire Chronicles)

In this classic parlor mystery from CWA Diamond Dagger winner Catherine Aird, Detective Inspector C. D. Sloan investigates a dinner party that ended in murder

Twelve friends sit down for supper at Strontfield Park—but only eleven survive the evening. After dinner, the host, William Fent, offers to drive one of his guests home, only to die behind the wheel in a violent accident. The autopsy shows that Fent ingested enough barbiturates to kill a horse.
 
So begins a fresh tale of murder and deceit for Detective Inspector C. D. Sloan, whose list of suspects begins and ends with the surviving dinner guests. Among them are a theologian at the local university; Dr. and Mrs. Washby, whose wedding was the cause for celebration; Ursula Renville, tall, graceful, and utterly aloof; the fat and extravagant Mr. and Mrs. Marchmont; the spinster Miss Paterson; the rector’s daughter, Cynthia Paterson; Quentin Fent, heir to the Fent fortune; and Mr. Fent’s wife, the now-widowed Helen. Each of the guests had the opportunity to kill William Fent. But which one wanted him dead?