Angela Smithers prided herself on her rational, sensible approach to life. She was the sort of woman who arranged her spice rack alphabetically and could recite the precise date on which she'd last had her car's oil changed. She wore cardigans even in July, and kept her golden retriever, Waffles, on a strict schedule of morning walks and evening snuggles. To the outside world, she projected calm stability, the sort of woman who would never forget your birthday, who'd always have a spare umbrella, who could be depended on to keep her head when others were losing theirs.

Which was precisely why the arrival of the envelope—postmarked from Derbyshire, England, with a return address she didn't recognize—was so unsettling.