On a luxury cruise from Southampton to New York, the annual gathering of the mysterious Midnight Chorus Society is in full swing. Unbeknownst to the rest of the innocent passengers, the deadly convention is made up entirely of serial killers, wannabes and their fans. Travelling on board is Hollywood royalty Jacqui Dulac, star of the television show Lady Detective, and her latest ghost-writer, Martha Hammond. Yet when Martha witnesses a shocking murder on deck, with a single red button found near the crime scene, the quarrelling duo must put aside their differences to become real-life detectives... But with a cruise liner full of the world's most notorious serial killers, they both know that when there's been one murder, another is sure to follow. And as a storm rocks the ship, can Martha and Jacqui identify the killer before it's too late?