Jocelyn turns to the "country house party" trope in this entertaining Aggie Morton sequel (The Body Under the Piano, rev. 1/20). Twelve-year-old Aggie (loosely based on Agatha Christie) and her friend Hector Perot are spending Christmas at Owl Park, where Aggie's sister, newly a baroness, is learning to be mistress of a great house. The mystery begins when the other guests arrive. One guest, Lakshay Sivam, is carrying a possibly cursed emerald, which he plans to return to his native Sri Lanka; it disappears just as one of the actors hired to entertain the house party is murdered -- and then Lakshay goes missing. Although the police take charge, Aggie, Hector, and their new friend Lucy can't stop themselves from doing some investigating of their own. With a solidly plotted whodunit, Jocelyn keeps readers guessing through a complex cast of suspects, all with something to hide, and enough red herrings to keep any detective on her toes. Despite the high stakes, the book keeps a generally light tone, making for an enjoyable read. Jocelyn touches on deeper issues, including Aggie's concerns about her widowed mother's ongoing depression, but the action always takes center stage. Sarah Rettger January/February 2021 p.105(c) Copyright 2021. The Horn Book, Inc., a wholly owned subsidiary of Media Source, Inc. No redistribution permitted.