 Frank Sinatra, in his last major acting role (he planned to appear on "Magnum, P.I." again the following season, but Tom Selleck s scheduling conflicts forced the producers to cut back the episodes and Sinatra s turn never came) casts him as a retired New York cop who learns that his beloved granddaughter was kidnapped and murdered by incredibly vicious sexual predators during his retirement celebration. Sgt. Doheny eventually tracks the two killers to Hawaii and enlists Magnum s help without telling him why he wants to find the men. One of the killers flees Doheny and is run over by a bus. In a quiet, intense way, Doheny describes the killing to Magnum and makes it perfectly clear that he will kill the other murderer if he finds him, no matter what the circumstances. Magnum goes along hoping to find the killer first and spare Doheny from a murder rap.