Framed in the doorway of Poirot's bedroom stood an uninvited guest, coated from head to foot in dust. The man's gaunt face stared for a moment, then he swayed and fell. Who was he? Was he suffering from shock or just exhaustion? Above all, what was the significance of the figure four, scribbled over and over again on a sheet of paper? Poirot finds himself plunged into a world of international intrigue, risking his life to uncover the truth about "Number Four".

Nick Buckley was an unusual name for a pretty young woman. But then she had led an unusual life. First, on a treacherous Cornish hillside, the brakes on her car failed. Then, on a coastal path, a falling boulder missed her by inches. Later, an oil painting fell and almost crushed her in bed. Upon discovering a bullet-hole in Nick's sun hat, Hercule Poirot decides the girl needs his protection. At the same time, he begins to unravel the mystery of a murder that hasn't been committed. Yet.

Poirot had been present when Jane bragged of her plan to "get rid of" her estranged husband. Now the monstrous man was dead. And yet the great Belgian detective couldn't help feeling that he was being taken for a ride. After all, how could Jane have stabbed Lord Edgware to death in his library at exactly the same time she was seen dining with friends? And what could be her motive now that the aristocrat had finally granted her a divorce?

From seat No.9, Hercule Poirot was ideally placed to observe his fellow air passengers. Over to his right sat a pretty young woman, ahead, across the gangway in seat No.8, a detective writer was being troubled by an aggressive wasp. What Poirot did not yet realize was that behind him, in seat No.2, sat the slumped, lifeless body of a woman.

Mr Shaitana was famous as a flamboyant party host. Nevertheless, he was a man of whom everybody was a little afraid. So, when he boasted to Poirot that he considered murder an art form, the detective had some reservations about accepting a party invitation to view Shaitana's private collection.

Thirteen guests arrived at dinner at the actor's house. It was to be a particularly unlucky evening for the mild-mannered Reverend Stephen Babbington, who choked on his cocktail, went into convulsions and died. But when his martini glass was sent for chemical analysis, there was no trace of poison, just as Poirot had predicted. Even more troubling for the great detective, there was absolutely no motive.

An urgent cry for help brings Poirot to France. But he arrives too late to save his client, whose brutally stabbed body now lies face downwards in a shallow grave on a golf course. But why is the dead man wearing his son's overcoat? And who was the impassioned love-letter in the pocket for? Before Poirot can answer these questions, the case is turned upside down by the discovery of a second, identically murdered corpse.

Among the towering red cliffs of Petra, like some monstrous swollen Buddha, sat the corpse of Mrs Boynton. A tiny puncture mark on her wrist was the only sign of the fatal injection that had killed her.

Roger Ackroyd knew too much. He knew that the woman he loved had poisoned her brutal first husband. He suspected also that someone had been blackmailing her. Now, tragically, came the news that she had taken her own life with a drug overdose.

An outbreak of kleptomania at a student hostel was not normally the sort of crime that aroused Hercule Poirot's interest. But then he saw the list of stolen and vandalized items: a stethoscope, some old flannel trousers, a box of chocolates, a slashed rucksack, and a diamond ring found in a bowl of soup. The list made absolutely no sense at all. But, reasoned Poirot, if this was merely a petty thief at work, why was everyone at the hostel so frightened?

First there was the mystery of the film star and the diamond...then came the "suicide" that was murder...the mystery of the absurdly cheap flat...a suspicious death in a locked gun-room...a million dollar bond robbery...the curse of a pharoah's tomb...a jewel robbery by the sea...the abduction of a Prime Minister...the disappearance of a banker...a phone call from a dying man...and, finally, the mystery of the missing will.

Lucy Angkatell invited Hercule Poirot to lunch. To tease the great detective, her guests stage a mock murder beside the swimming pool. Unfortunately, the victim plays the scene for real. As his blood drips into the water, John Christow gasps one final word: "Henrietta". In the confusion, a gun sinks to the bottom of the pool. Poirot's enquiries reveal a complex web of romantic attachments. It seems everyone in the drama is a suspect, and each a victim of love.

Sir Claud Amory has discovered the formula for a new powerful explosive, which is stolen by one of the large household of relatives and friends. Locking everyone in the library, Sir Claud switches off the lights to allow the thief to replace the formula on the table, no questions asked. When the lights come on, however, he is dead.

A few weeks after marrying an attractive young widow, Gordon Cloade is tragically killed by a bomb blast in the London blitz. Overnight, the former Mrs Underhay finds herself in sole possession of the Cloade family fortune. Shortly afterwards, Hercule Poirot receives a visit from the dead man's sister-in-law, who claims she has been warned by "spirits" that Mrs Underhay's first husband is still alive.

The dentist was found with a blackened hole below his right temple. A pistol lay on the floor near his out-flung right hand. Later, one of his patients was found dead from a lethal dose of local anaesthetic. It's a clear case of murder and suicide. But why would a dentist commit a crime in the middle of a busy day of appointments? A shoe buckle holds the key to the mystery. Now, in the words of the rhyme, can Poirot pick up the sticks and lay them straight?