Based on the TV series the film follows DI Regan and DS Carter as they became embroiled in a deadly political scandal. One of the leading members of the government, Charles Baker (Ian Bannen) is about to secure a huge deal with OPEC stabilising the world oil market and boosting Britain's position within it. Baker is the rising star of government, regarded a future prime minister, who is closely controlled by his urbane, manipulative American press secretary Elliot McQueen (Barry Foster). When Regan investigates the mysterious death of a prostitute as a favour to one of his informants, he becomes aware that Baker and McQueen might be involved. A spate of killings follow - which sees Regan take on both the criminals and the hierarchy of the Metropolitan Police and British security services.\
Actress Jane Wilkinson wants a divorce, but her husband, Lord Edgware, refuses. She convinces Hercule Poirot to use his famed tact and logic to make her case. Lord Edgware turns up murdered, a well-placed knife wound at the base of his neck. It will take the precise Poirot to sort out the lies from the alibis - and find the criminal before another victim dies.