A Death After Dinner - David S. Pederson

England, 1951. Black tie, French champagne, and a pinch of poison. 

Sir Roderick and Lady Endicott have planned a pleasant weekend for their family and friends at their sprawling country estate. Scandal is the last thing on the menu, but tempers simmer as difficult and disliked decorator Oscar Maxwell joins the party. By the time he suddenly drops dead after dinner, no one is exactly sorry.

As the local inspector determines poisoning, suspicion falls on a charming and secretive man close to Lady Endicott's brother, Professor Liam Cuthbert. Liam must wade through a tangle of secrets, rivalries, and outright loathing to get to the truth. Someone at the table is a killer, and if Liam doesn't find them soon, an innocent man could be sent to the gallows.