Sir Laurence Olivier is making a movie in London. Young Colin Clark, an eager film student, wants to be involved and he navigates himself a job on the set. When film star Marilyn Monroe arrives for the start of shooting, all of London is excited to see the blonde bombshell, while Olivier is struggling to meet her many demands and acting ineptness, and Colin is intrigued by her. Colin's intrigue is met when Marilyn invites him into her inner world where she struggles with her fame, her beauty and her desire to be a great actress.

This is a dramatisation of the true story of Major Herbert Rowse Armstrong, a solicitor and magistrate's clerk who lived in the small Welsh town of Hay-on-Wye. In 1921 he was arrested and charged with poisoning his domineering wife, Catherine, and later attempting to poison a business rival, Oswald Martin, by administering arsenic to them. At his trial, Armstrong claimed that he had bought the arsenic simply to kill the dandelions on his lawn. However he was convicted of murder and executed in 1922.