Recovering from the horrors of World War I, British Army officer Arthur Hastings hopes to find peace and quiet at a country manor in the English countryside. But when the matriarch dies during the night from strychnine poisoning, Hastings enlists the help of an old friend staying nearby with other war refugees to help solve the murder: former Belgian police detective Hercule Poirot.

Suggestions of a Communist conspiracy cast suspicion on a murdered woman's Russian servant. Meanwhile, Poirot has a rose named after him, and a ceremony at the Chelsea Flower Show makes him the centre of attention. Hastings receives a packet of seeds and develops hay fever.

The London and Scottish Bank is sending a huge shipment of Liberty Bonds to New York on the liner Queen Mary. Poirot, who suffers terribly from sea-sickness, is asked to see the bonds safely across the Atlantic.

An Australian shipping tycoon wants Poirot to check out his daughter's suitors. Then the young lady takes a trip on the Plymouth Express, and Poirot finds himself investigating a jewel theft on the train.

Poirot visits a garden fete, where a wasps' nest adds to the tension. He meets the son of an old friend who has his girl-friend, a fashion model, with him, and Poirot soon suspects that they are both in danger. He has to solve a mystery which includes cyanide, failing brakes and mixed-up love lives. Meanwhile, Hastings has a new hobby which Poirot finds helpful in cracking the case.

Poirot is summoned to Marsdon by the owner of a country inn there to solve a murder. But the inn-keeper is a would-be thriller writer, and to Poirot's dismay the murder turns out to be fictional. Thankfully, though, there is soon a real (if seemingly supernatural) murder at the big house. Things get even more interesting when a young wife claims that a tree in her garden is haunted by a laughing ghost, and there are also signs of black magic from East Africa. Poirot lays a clever ambush to smoke out the killer,confident that he or she will turn out to be human.

Japp (who is really worried that failure could cost him his job) seeks Poirot's help in investigating a series of jewel thefts, and two remarkable things happen. Poirot falls in love (with the beautiful and clever Countess Vera Rossakoff) and he also meets a criminal intellect which he finds worthy of him. As the countess is his main suspect, Poirot spends most of his time with her - which for once leaves Hastings and Miss Lemon to do most of the actual detective work.

In the end, this case may have to be put down as the one that got away.

Poirot is called in to help a woman who lives in fear of her husband, and he is invited to a dinner party which goes horribly wrong.

Poirot prepares to spend a quiet Christmas on his own with a box of chocolates, but he has to give up his plans when the British government asks for his urgent help. Prince Farouk, a young member of the Egyptian royal family visiting London, has lost a famous ruby, and this is deemed to be a matter of national security.

Poirot attends the Victory Ball, a costume party where you are expected to dress as someone famous, as himself. However, when two members of a party of six dressed as characters from classical Italian comedy are subsequently found dead, Poirot finds himself working with Chief Inspector Japp to solve the case. The solution to the deaths of Viscount Cronshaw and Coco Courtney is to be found in determining the correct time of death and identifying an impostor at the ball. Poirot takes to the airwaves and reveals the identity of the killer on a live BBC radio broadcast.