Envious Casca, by Georgette Heyer

If you find Georgette Heyer's best-known romance novels, to borrow a phrase from Jane Austen, rather too light and bright and sparkling, her mysteries are considerably nastier. Heyer had a gift for creating caustic, almost misanthropic characters, and nowhere is this displayed to better effect than in the pages of Envious Casca, her 1941 locked-room whodunit.

Envious Casca is set during a perfectly disastrous Christmas party. A mixture of family and business associates have gathered to celebrate the holiday at the home of Nat Herriard, a wealthy and irascible bachelor. As Nat keeps reminding everyone, the party wasn't his idea—it was organized by his sweet yet sadly tactless younger brother. After a particularly hellish evening gathering, Nat furiously locks himself in his study, where he is eventually found, dead from a stab wound in the back. The police have no idea how the murderer managed to kill a man in a sealed room, but there's no shortage of suspects: nearly everyone in the house wanted Nat dead.

If you're an expert on either Julius Caesar or the House of Habsburg, you're going to find it pretty easy to solve this mystery. But even if you've picked out the murderer by the end of the first chapter, the real joy of this novel comes from its characters—a melodramatic actress, a wildly over-sensitive playwright, a dim-witted vamp, a stoic former chorus girl, a shady businessman, and the not-very-romantic pair at the center of the story: Nat's bitter nephew Stephen, and Matilda, a distant cousin who is the only person the reader can be sure isn't the murderer. This precisely-drawn, character-driven story makes for a richly satisfying read, and is the perfect story to get you through your own unpleasant holiday gathering. Because no matter how bad your relatives are, Heyer's creations are almost certainly worse.