John F. Donovan (Kit Harington) is an American TV and film star who struggles with his public image. He has a girlfriend (Emily Hampshire) for show, but a secret lover (Jared Keeso). When John dies alone and unexpectedly following a series of scandals, one fan in particular, 11-year-old Rupert Turner (Jacob Tremblay), has insight into John's soul, because for five years the two were secret pen pals. The letters helped Rupert get through tough times as he faced bullies while his mother (Natalie Portman) had no idea about his correspondence with the celebrity.

Now an adult, Rupert (Ben Schnetzer) has become a successful actor himself, as well as an author as he pens a memoir about his correspondence with John. In an interview with reporter Audrey Newhouse (Thandie Newton), Rupert reveals everything he knows about John's troubled life, what compromises John made for fame—and how John's tenderness and generosity inspired that troubled little boy who was desperate to connect with the man he idolized.