"When "The Russian Pink"—a stunningly large rose-hued diamond—makes a surprise appearance around the neck of Honey Li, the wife of surging presidential candidate Harry Nash, Alex Turner, an investigator for the Treasury Department's diamond division and former C.I.A. agent, finds himself spiraling down a seemingly endless rabbit hole. A diamond like that always carries secrets, but the web of mystery behind "The Pink" is more complex than Alex could ever image."