In 2004, Mortimer played the lead role in the drama "Dear Frankie", about a young mother whose love for her son prompts her to plan a deception to protect him from the truth about his father. Her performance gained positive reviews; "San Francisco Chronicle" wrote, "an unforgettable performance from Mortimer [...] a leading lady". Matthew Leyland of the BBC gave the film 3 out of 5 stars, and was impressed with Mortimer's performance, which was played with "heartfelt conviction". In an interview with critic Roger Ebert, Mortimer said, "I seem to find characters who are held back and guarded, physically and mentally. It's a relief after the film is over. [...] But when I'm acting, it's good to have something to play against, boundaries to break."