All the "In Death" Eve Dallas stories have the author on the cover: "Nora Roberts writing as J. D. Robb". This one has "Nora Roberts and J. D. Robb". Not since John Wyndham and Lucas Parkes wrote The Outward Urge have I read a book by two authors who are in fact the same person. The reason here is simple: this is a book of two halves. The first, set in contemporary small-town America, revolves around a $28M diamond heist, insurance investigator Max Gannon, and antique shop owner Laine Tavish, who just happens to be the estranged daughter of one of the thieves. The second half is set 50 years later in Lt Eve Dallas' New York, where murder strikes again as clues to the lost diamonds' whereabouts begin to appear.
Roberts' story of Max and Laine sets the scene for Robb's Dallas story. Although the events are linked through time, each half reads like a separate short novel. And quite clearly written by the same person: Roberts doesn't use a pseudonym to signal a change in writing style, but rather to label a particular series, it seems.