I've Got You Under My Skin by Mary Higgins Clark

In this gripping suspense novel, a television producer named Laurie Moran is determined to solve a cold case murder for her new reality show, "Under Suspicion." The case revolves around the unsolved murder of a wealthy socialite, Betsy Powell, who was killed during a party celebrating her husband's acquittal. As Laurie gathers the original party guests for a reunion, tensions rise and secrets unravel, revealing that each guest harbors hidden motives and dark pasts. As the investigation unfolds, Laurie finds herself in a dangerous web of deception, where the killer is closer than she ever imagined.

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