It is a golden evening of high summer in July 1990. Robin Timariot has set out that morning on what he has planned as a six-day tramp along part of Offa's Dyke. At the close of his first day's walk he encounters an elegant middle-aged woman who seems strangely out of place among the sheep and gorse of Hergest Ridge. They exchange only a few words of conversation, but their talk is enigmatic -- and unforgettable. A few days later, at the end of...