As Hercule Poirot sifts through his post one particular morning, he alights upon a letter from an elderly and (as it transpires), exceedingly rich spinster - Miss Emily Arundell. She is clearly in great distress and seeking his help, but doesn't say why. Her only specific mention is 'the incident of the dog's ball'.
The first message sent to Tom Thorne's phone was just a picture - the blurred image of a man's face, but Thorne had seen enough dead bodies to know that the man was no longer alive. But who was he? Who sent the photograph? And why? While the technical experts attempt to trace the sender, Thorne searches the bulletins for a reported death that matches the photograph. Then another picture arrives.