Helena Campbell (Stephanie Leonidas) works in the circus with her parents Joanne (Gina McKee) and Morris (Rob Brydon), but she wants to leave. After an argument with Helena, her mother collapses and is taken to the hospital. Ten days later, living with her grandmother, Helena learns that her mother needs an operation and she blames herself.
That night, she gets out of bed and sleepwalks outside, where three performers are going through their paces for her, until a shadow falls over them and two performers are consumed. The third, a juggler named Valentine (Jason Barry), directs Helena to safety with magical flying books. They find themselves in the City of Light, in a strange world filled with magical creatures which is being destroyed by shadows. Its denizens are fleeing in terror. Helena is mistaken for a princess and she and Valentine are taken to the Prime Minister (also Rob Brydon), who explains that the princess from the Land of Shadows stole a charm from the White City, leaving the Queen of Light (also Gina McKee) in deep sleep and the city vulnerable to the creeping shadows. Noticing the Royal Family’s resemblance to her parents, she offers to help recover the charm. But the Queen of Shadows (also Gina McKee) is watching, thinking that Helena is her daughter.
Helena and Valentine try to stay ahead of the shadows and follow the clues to the charm, called Mirrormask. When Helena looks through the windows of the city, she can see into her own bedroom, looking through the drawings on the wall. She sees herself living there and behaving strangely. Her other self notices her and starts to destroy the drawings, causing parts of the fantasy world to collapse. Valentine betrays Helena to the Queen of Shadows in exchange for jewels. The Queen’s servants begin to change Helena’s mind, making her think she is the Princess of Shadows. Valentine comes back and helps Helena break the spell with juggling. They search the Princess’ room and Helena finds the Mirrormask hidden in the Princess’ mirror and they escape with it.
As they arrive at Valentine’s tower, Helena realizes that the other Helena is the Princess of Shadows, who entered her room through the Mirrormask. The Princess destroys the rest of the drawings and Helena cannot return. Helena and Valentine start to disappear. The Princess takes the drawings to the roof to cast the shards to the wind, but there is one more drawing on the back of the roof door. Through it, Helena returns to the real world and sends the Princess back to the other. The Queen of Light awakes and the two cities are restored. Helena wakes up on the roof and she and her father learn that her mother’s operation was successful. Helena returns to the circus and notices a juggler who looks like Valentine.
This gorgeously surreal, though a little slow, film was designed and directed by Dave McKean and written by him and comic-book author Neil Gaiman from a story they created together. It was produced by the Jim Henson Company to be a direct-to-video film but had a limited run in the theaters. It received positive reviews at the Sundance Festival. The animators were all from the same art-school and knew each other well. The music was by circus composer Iain Balamy. The film was nominated for the—wait for it—William Shatner Golden Groundhog Award for Best Underground Movie. A children’s book was based on it and Dark Horse Comics released some Mirrormask merchandise—a version of the Really Useful Book that appears in the film and figures of characters in the movie. The computers used to do the CGI were named John, Paul, George, and Ringo, but when they added Yoko they all crashed.