Perhaps his best-known books are The Seventh Swan and Grimbold's Other World. Gray often produced adaptations or continuations of traditional fairy tales and fantasy works, as in his Further Adventures of Puss in Boots. His The Stone Cage is a re-telling of Rapunzel from a cat's point of view. Over The Hills to Fabylon is about a city whose king has the ability to make it fly off across the mountains if he feels it is in danger.
Gray maintained a long-term collaborative relationship with set designer and illustrator Joan Jefferson Farjeon (sister of Eleanor Farjeon and Harry Farjeon); she supplied the costume and scenic designs for many of the theatrical productions of his plays, as well as the illustrations of his books.