Elinor Carlisle is tried for poisoning Mary Gerrard, the young woman whose presence threatened both Elinor’s inheritance and her engagement to Roddy Welman. The evidence appears direct: Elinor prepared the final meal, possessed a clear motive and was present when Mary died.
Asked to investigate before the verdict, Poirot reconstructs events around the illness of the wealthy Laura Welman and tests the medical and emotional assumptions supporting the prosecution. The novel combines courtroom suspense with a study of class, romantic humiliation and the dangerous certainty that an apparently comprehensible motive proves guilt.