One Fearful Yellow Eye — John D. MacDonald

How do you extort $600,000 from a dying man? Someone had done it very quietly and skillfully to the husband of Travis McGee's ex-girlfriend. McGee flies to Chicago to help untangle the mess and discovers that although Dr. Fortner Geis had led an exemplary life, there were those who'd take advantage of his one "indiscretion" and bring down the whole family. McGee also discovers he likes a few members of that family far too much to let that happen...

TRAVIS McGEE
Part rebel, part philosopher, and every inch his own man, Travis McGee is the rugged, sexy Florida boat bum with a special genius for helping friends in trouble--or avenging their deaths.