This cautionary episode of Behind the Music documents the growing menace of stalkers. Considered by some the "prototype" for fans who take their celebrity obsessions to dangerous and often criminal extremes, John Lennon's murderer, Mark David Chapman, is the focus of this investigative piece. With a detailed account of the events of the day he shot the former Beatle; to interviews with Chapman conducted during his prison sentence; comments from his psychiatrist and the photographer who caught Lennon and his killer on film; BTM paints a frightening picture of a deranged individual who is up for parole this year. Security consultant Gavin de Becker outlines warning signs. Lilith founder Sarah McLachlan comes forward about her own terrifying experience and the song ("Possession") that came out of it. Two real-life stalkers explain their motivations. Bjork's victimizer records himself on video just moments before his suicide.