Lord Sunday is the seventh book concluding Garth Nix's The Keys to the Kingdom series. The book was released on 1 February 2010 (Australia). The description reads "Arthur Penhaligon must complete his quest to save the Kingdom he is heir to... and Arthur's world." The book was the number 14 top selling book in Australia during its launch week.
The book was released in Australia on 1 February 2010, the U.K. on 4 March 2010, and the U.S. on 16 March 2010.