Cleo's holiday with her family to the seaside resort town of Brighton is everything she hoped it would be...until she receives a blackmail note. The blackmailer demands Cleo help her or a story revealing Cleo's investigating will appear in the newspaper. With her uncle warning her to keep her detecting activities private, Cleo agrees to meet the blackmailer when they return to London. But when the woman is seen getting on the train but not off, Cleo grows concerned.

She enlists the help of the hotel staff to search for the body along the railway line. Finding it confirms her suspicions and leads her to discover that her blackmailer was a gossip columnist. What scandal had the victim uncovered that led to her death? And which fellow passenger had a secret worth killing for?

With Harry Armitage's assistance, Cleo attempts to track down the murderer. Meanwhile, pressure is mounting on the hotel staff to host a society wedding that will be featured in the social pages for all the right reasons.