One Fearful Yellow Eye by John D. MacDonald

MacDonald is an odd writer that so far is worth the read. PW How to you extort $600,000 from a dying man? Someone had done it very quietly and skilfully 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 one "indiscretion" and bring down the whole family. McGee also discovers he likes a few members of the family far too much to let that happen....