Geïnspireerd door het gezegde "Olifanten vergeten niet" slaagt Hercule Poirot erin een groot aantal feiten te achterhalen, waardoor duidelijk wordt op welke wijze twintig jaar tevoren een echtpaar om het leven kwam.
This is the diary of Cassandra Mortmain, which tells of her extraordinary family and their crumbling castle home. Cassandra's father was once a famous writer, but now he mainly reads detective novels while his family slide into genteel poverty. Her sister Rose is bored and beautiful, and desperate to marry riches. Their step-mother Topaz has habit of striding through the countryside wearing only her wellington boots. But all their lives will be soon be transformed by the arrival of new neighbours from America, and Cassandra finds herself falling in love.