At 2 a.m. on the morning of her fortieth birthday, Sophie wakes to find an intruder in her bedroom. The stranger hands Sophie a letter and issues an threat: open the letter at her party that evening, in front of family and friends, at exactly 8 p.m., or those she loves will be in grave danger.

What can the letter possibly contain?

This will be no ordinary party; Sophie is not the only person keeping a secret about the evening ahead. When the clock strikes eight, the course of several people's lives will be altered for ever.