Billionaire media mogul Bill Parrish is considering a merger between his company and another media giant and is about to celebrate his 65th birthday with an elaborate party planned by his eldest daughter, Allison. His youngest daughter, Susan, a resident in internal medicine, is in a relationship with one of Bill's board members, Drew. She is considering marriage, but Bill can tell that she is not passionately in love. When she asks for the short version of his impassioned speech, he simply says, "Stay open. Who knows? Lightning could strike!". When their company helicopter lands, he begins to hear a mysterious voice, which he tries with increasing difficulty to ignore.
Susan meets a vibrant young man at a coffee shop. He takes an interest in her and tells her that lightning may strike. She is enamored but parts without getting his name. Unbeknownst to her, the man is struck by multiple cars in a possibly fatal collision.
Death arrives at Bill's home in the uninjured body of the young man, explaining that Bill's impassioned speech has piqued his interest. Given Bill's "competence, experience, and wisdom", Death says that for as long as Bill will be his guide on Earth, Bill will not have to die. Making up a name on the spot, Death is introduced to the family as "Joe Black".
Bill's best efforts to navigate the next few days, knowing them now to be his last, fail to keep events from going rapidly out of his control. Drew is secretly conspiring with a man bidding for Parrish Communications. He capitalizes on Bill's strange behavior and unexplained reliance on Joe to convince the board of directors to vote Bill out as chairman, using information given to him inadvertently by Bill's son-in-law, Quince, to push through approval for the merger which Bill had decided to oppose. Quince is devastated.
Susan is confused by the appearance of Joe, believing him to be the young man from the coffee shop, but eventually falls deeply in love with him. Joe is now under the influence of human desires and becomes attracted to her as well. After they make love, Joe asks Susan, "What do we do now?" She replies, "It'll come to us". Bill angrily confronts Joe about his relationship with his daughter, but Joe declares his intention to take Susan with him for his own.
As his last birthday arrives, Bill appeals to Joe to recognize the meaning of true love and all it encompasses, especially honesty and sacrifice. Joe comes to understand that he must set aside his own desire and allow Susan to live her life. He also helps Bill regain control of his company, exposing Drew's underhanded business dealings to the board by claiming to be an agent of the Internal Revenue Service and threatening to put Drew in jail.
