The book contains a series of short mystery cases narrated mostly by Captain Hastings, Poirot's loyal friend and companion. Each chapter presents a different crime or puzzle — including murders, robberies, kidnappings, disappearances, and strange mysteries — which Poirot solves using logic, observation, and psychological insight. Rather than relying on violence or action, Poirot depends on his brilliant mind and his famous little grey cells to uncover hidden truths and expose criminals. The stories take place in elegant English settings and involve wealthy families, secret motives, stolen jewels, suspicious servants, false identities, and carefully concealed clues. Christie combines suspense, humor, and clever plotting, often ending each case with an unexpected revelation.