Akuyaku Reijou? Iie, Gokuaku Reijou desu wa

Rosalia is secretly feared as a 'heinous young noble lady' and lives confined to only the Marquis' residence. One day, she tells her grandfather, "I fell in love with a knight who wandered into the garden, Kadeo." However, this is just a convenient excuse so she can leave her confined life on the residence for the outside world, or is it...?