Lady Rose MacClare

Rose arrives at Downton as a teenage cousin packed off to the Crawleys, ostensibly to be presented at court but really to be kept out of trouble. She is restless, thrilled by jazz and dancing and anything her family disapproves of, and treats the strict rules of the house as a challenge rather than a boundary.

Lily James plays her with such unguarded delight that Rose never curdles into a mere cautionary tale about flappers. The scripts use her to let 1920s modernity crash into the Abbey's Edwardian order, and James makes every scrape feel like genuine appetite for life rather than performed rebellion, which is what makes the adults' exasperation so funny.