Just another GR refugee. Other than that, I had a stroke in 2004, and read almost anything I can get my hands on, though I have a particular weakness for history, mystery, and historical fiction.
In The Affair of the Blood Stained Egg Cosy (and one does actually appear in the novel!), it is the late 1930s, and a central european duchy is worried about Hitler. They are negotiating with the British government over the terms of protection, and have agreed to send two senior diplomats to England, to hash out details. To keep things quiet at this stage, the meetings are to be held at an English country house, under cover of the family having a weekend party, where the daughter's friends will be present, along with an American millionaire and his wife, the guests of the earl. (The earl, and the millionaire, Mr. Peabody, are both notable collectors of antique guns.)
Then valuable antique pistols are stolen, as are Mrs. Peabody's spectacular diamonds, and another guest's body is found in a lake. The police are called in.
Most of these characters have secrets, hardly anyone is telling the truth at any given time, and the plot is highly twisted (I certainly didn't guess who did it).
The clues are fairly laid, but I would suggest that what isn't said is almost as important a clue as what is, to what is actually going on. ("The silence of the dog in the night," in a way.)
A nice little historical mystery.