Grand Duke, There Is an Outsider Among Us

ATEEZ's SAN and Han Ji Eun join the members as a grand duke and princess in a race to unite a divided kingdom. The three grand dukes face a crucial mission to identify the outsiders hiding among them. As trust gives way to suspicion, the members must figure out who truly belongs to each realm. Can the grand dukes expose the outsiders, reunite their kingdoms, and avoid the penalty?