With their glossy brown hair and hazel eyes, best friends Princess Millie and maid Jess look so similar that they often trade places. They love swapping clothes and tricking everyone in the palace, and while Jess enjoys attending Millie's dance lessons, the princess happily bakes cakes in the royal kitchen.Preparations are underway for Prince Edward's first birthday celebrations. In keeping with tradition, he will wear the Baby Diamond Crown at the party, but when it goes missing, a frantic search of the palace ensues. Millie and Jess team up to examine the clues and solve the mystery of the crown's disappearance, but can the young sleuths find the thief before the birthday party begins?