Georgette Heyer wrote almost 50 genre novels - Regency romance, historical, and detective fiction. The Unfinished Clue is a classic English country house murder detective story. First published in 1934, the story features contemporary characters packed into the country home of General Sir Arthur Billington-Smith, a right hard bastard that no-one is sad to find dead, except for those trying to get his money. With lots of motive, and no clear alibis, the guests are stuck hanging about the Grange, as the mansion is called, while a Scotland Yard detective is put on the case to interview them one-by-one.
The characterizations and dialog are sparkling. Heyer includes a sub-plot of romance for the one known innocent, Miss Dinah Fawcett, a 'spinster' (in her own words) at twenty five. The game of guess the murderer is kept going up to the last few pages, befitting any good mystery. Any devoted reader of mysteries knows to throw out the obvious choices, including the butler, right away. Choosing an unlikely character with no clear motive at the start of the novel pays off in the end, when the author reveals that you were correct in your guess.
Of course, the combination of unlikable bastard victim, unlikable minor character responsible and brought to justice, and successful love affair for main character makes this a novel that is not going to challenge the reader significantly. This is not hardboiled detective noir. You are here to get entertained in an enjoyable way, not forced to think deeper than 'whodunit?' And I did enjoy reading The Unfinished Clue. Heyer sends up English manners, skewers affectations, and pops the bubble of the pretentious with relish. Her strong central female could use a little more witty repartee and smoldering glances before falling into the arms of Inspector Harding (and she doesn't solve the case before he does), but on balance this is a minor issue.
If you are interested in genre writing, I would recommend reading more of Georgette Heyer. Certainly I plan to populate my Nook with more of her stories. As Isaac Asimov's R Daneel Olivaw detective stories show, it is possible to transplant some of the conventions of country house mystery to fantasy and science fiction settings. Heyer is also lauded for her historical research and detail, and credited by some with inventing the Regency romance category in the 20th century.
Fun, and recommended.