Come to Grief - Dick Francis

Sid Halley, the ex-champion jockey turned investigator who appears in Odds Against and Whip Hand, is back. In Come to Grief he faces new dangers, new deeply demanding decisions.
Sid has uncovered an obnoxious crime committed by a friend whom he—and everyone else—has held in deep affection. On the morning set for the opening of the friend’s trial, at which Sid is due to be called as a witness, other people’s miseries explode and send him spinning into days of hard rational detection and heart-searching torment.
Troubled, courageous and unwilling to admit defeat, for Sid Halley it is business as usual