A mousy, secretive researcher at a news-clipping service who recently won $20,000 on "Jeopardy!" is missing. Who is Irene March? That's the answer (in the form of a question) facing investigator Jane da Silva, who can collect on her eccentric uncle's vast legacy only when she solves a mystery that's stumped everyone else. When Jane places a large "Have you seen this woman?" ad in the Seattle paper, she gets intriguing responses from a rodeo queen,...