The Mysterious Affair at Styles is a time capsule in another sense as well. It's Christie's first novel, published in 1920 and set during World War I. While on sick leave after being injured on the front, Captain Hastings runs in to an old friend, Lawrence Cavindish, who invites him to stay with him at his stepmother's estate. A country estate owned by a widow recently remarried to an unsuitable man, what could possibly go wrong? The characters may have been surprised when Lawrence's stepmother died, apparently poisoned by her evening coffee, but readers expect it. We also expect that everyone - her husband, her stepsons, her secretary, her daughter-in-law, and her "poor relation" (who works in a hospital dispensary) - has a motive and opportunity. Only Captain Hastings and a Belgian refugee of his acquaintance (Hercule Poirot, of course) escape suspicion, and they solve the case.
What struck me on this reading was how although this was Christie's first novel, her formula was clearly set. Hastings bumbles through the case, the innocent cast suspicion upon themselves while covering up lesser secrets, and the evidence clearly supports the surprise ending. The Mysterious Affair at Styles feels like the work of a long established writer, hinting at Dame Agatha's enduring career.