At a village fête, Poirot runs into an old friend, John Harrison and his fiancé, Molly Deane, a fashion model. Harrison invites Poirot and Hastings to tea the following week where Poirot learns that Molly had once been engaged to a local artist, Claude Langton. However, Poirot is puzzled by a number of apparently unrelated incidents, such as Harrison’s sudden change in behavior and the mysterious disappearance of some items from their home.
Poirot begins to suspect that someone is being untruthful, and he believes that a murder is being planned. To investigate further, Poirot uses his newfound hobby of photography to document every detail of the scene. He captures images of Harrison’s strange behavior, the suspicious movements of Molly, and the mysterious disappearance of the items.
As the days pass, Poirot uncovers more evidence of deception and lies. He sees Harrison secretly communicating with someone who has access to the locked room where the items were hidden. Additionally, he observes Molly making secret phone calls to someone she claims is her cousin.
Finally, on the day of the fête, Poirot discovers the truth behind all the lies. He sees Harrison and Molly having an intimate moment, unaware that cameras are recording them. The couple reveals that they were actually engaged to another man, not Claude Langton, and that their engagement was only a sham to cover up their affair.
With this information in hand, Poirot confronts the couple, revealing their deceit and arresting them for the crime of fraud. In addition, he takes custody of the stolen items and returns them to their rightful owners.