I was covering a street shooting for the Daily Bulletin when I met her. It was pure luck, but isn't half of life just luck? She lives above a retired Art Deco theater in San Francisco's Sunset District with an old long-haired cat, her harpsichord and enough yarn to fill a railroad car. The police call her their Yarn Woman. Her specialty is the forensic study of textiles. But they ask for her help with some trepidation because they know that whatever crime she's unraveling for them comes with a lot of knots and baggage. And ghosts. There are always the ghosts. This collection, "The Yarn Woman," includes our first three cases together. - Nat P.M. Fisher