Client Privilege - William G. Tapply

When someone tries to blackmail an old friend, Boston attorney Brady Coyne intervenes—only to wind up a murder suspect in this "solidly appealing series" (Publishers Weekly).
Brady Coyne has known Chester "Pops" Popowski since law school. An honest, battle-hardened Massachusetts judge, Pops is more soldier than scholar—and has been known to defend what's right with his fists. After years on the bench, Pops has been nominated for a federal judgeship, with a possible Supreme Court appointment in his future. Only one thing stands in his way: blackmail.
A TV reporter has evidence of a long-ago affair Pops conducted with a younger woman. Pops sends Brady, his genteel Boston lawyer, to tell the reporter he won't be getting any money. Soon after their meeting, the blackmailer is found dead. Brady refuses to name his client, and finds himself under suspicion of murder. Brady will do whatever it takes to keep Pops out of the papers. If he's lucky, he may even keep himself out of jail.