The Dick Francis Collection   Three intriguing racetrack mysteries   Former champion jockey Dick Francis invented his own genre of mystery-thriller when an accident cut short his riding career. No longer able to perform at the track, he began writing about it, using jockeys and other track types to show what went on behind the scenes, where murder and mystery were as prevalent as horses and hay. Here's three fan favorites.   Nerve Someone is trying to destroy the lives of jockeys all over England. When Jockey Robert Finn becomes the next target, he takes it upon himself to do a little amateur sleuthing to settle the score. (published in 1964)   In the Frame Charles Todd is an English artist who is well known and respected for his renderings of sleek and athletic horses. What he now faces at his cousin Donald's house is also art--the art of a perfectly brutal murder. (published in 1976)   Reflex When jockey Philip Nore begins to suspect that a track photographer's fatal accident was really murder, he sets out to discover the truth and to trap the killer, and unwittingly sets himself up to become the hunted rather than the hunter. (published in 1980)