There are winged horses in the mirrors of Briar Hill that only Emmaline can see. Briar Hill used to be the home of a princess, but is now a hospital for kids sick with TB during WWII. Emmaline spends her days quietly drawing with her friend Anna and trying to convince the other children that the horses are real. Then one day she goes into one of the off limit gardens and finds a wounded winged horse. It appears the Horse Lord has sent her to this world to recover but she is being hunted by the black horse. Emmaline must build a rainbow shield to protect Foxfire in the garden. But Emmaline and the other children are very sick and complications arise. 

This is one of those books that kind of sticks with you. I wonder if the horses were real or just part of Emmaline's fantasies. Emmaline keeps a lot of secrets from others and most especially from herself which makes the story even more interesting.