In 2010, miners retrieved a black opal from the Welo mine in Ethiopia. Two years later, the opal has made its way into the possession of Howard Ratner, a gambling addict who runs a jewelry store in New York City’s Diamond District. Basketball star Kevin Garnett takes an interest in the opal, asking Howard for it as a good luck charm for his next game. Howard agrees, keeping Garnett’s 2008 NBA Champion ring as collateral. Howard then proceeds to pawn the ring, kickstarting a chain of events that may very well spell his doom.
On his 85th birthday, mystery novelist Harlan Thrombey invites his family to his mansion in the state of Massachusetts. Things take a turn for the worse when the wealthy novelist is found dead with his throat slit. The police believe it to have been suicide, but in order to get to the bottom of things, an anonymous person hires a private eye by the name of Benoit Blanc to investigate. As the mystery unfolds, a picture will be painted of a dysfunctional family, and in the middle of this strife stands a nurse named Marta Cabrera.