Kit is building a sandcastle on the beach, with the help of his younger sister, Anna. It turns out that Anna is quite an expert on castles, and she reminds Kit of all the details he has forgotten - the dungeon, the keep, the stables and all the rest of the buildings that should be part of a castle. That night Kit dreams about being king of a real castle, but finds in his dream that Anna is the Queen of the Castle instead. The next day there is a sandcastle competition - but is Kit and Anna's castle good enough to win? Only when they decide to make it a thoroughly modern castle...