The Summons by John Grisham

Ray Atlee, a law professor, is brought back to his hometown to discuss his dying father's will and estate. When he gets there though, he finds his father dead in his study and a very large sum of money that isn't part of his father's will and estate. He figures that his father possibly couldn't have made that much money in his lifetime as a judge and thinking that it was probably dirty money. Knowing that most of the money would be taken away by taxes if he added it to his father's estate, he takes the money without telling anyone about it. When Ray is followed though, he realizes he's not the only one who knows about the money.