An Old Pureblood Tradition

Professor Harry Potter often used the Marauder's Map when patrolling Hogwarts during the night. He wasn't very pleased when, one day, he found the dots of Rose Potter, his daughter and Frank Longbottom II, his godson, together in a broom cupboard. Harry could have reacted in many ways but Marauder blood won out and decided to prank them. The thing is that Rose is also a Marauder...