When race caller and television presenter Mark Shillingford calls a race in which his twin sister, Clare, an accomplished and successful jockey, comes in second when she could have won, he believes the that she lost on purpose, and the race was fixed. That night, Mark confronts Clare with his suspicions, she storms off after an argument—and it’s the last time Mark sees her alive. Hours later, Clare jumps to her death from the balcony of a London hotel . . . or so it seems.

Devastated and guilty over her death, Mark goes in search of answers. What had led Clare to take her own life? Or was it not suicide at all?