The Mandeville Talent — George V. Higgins

Joe Corey, a promising young Manhattan attorney, gets drawn into an unsolved murder that happened 23 years ago. It's against his better judgment, but this is no ordinary crime. The victim is his wife's grandfather, Jim Mandeville, once president of a small-town New England bank.
What was it that compelled Mandeville to go to the bank at 5:30 that cold December morning to be killed by his own 12-gauge shotgun? It's up to Corey and his flamboyant sidekick, Baldo Lanucci, retired intelligence agent, to reheat cold leads -- and when they do, things turn hotter than anyone ever expected!