Humiliating a classmate is always a cause I can get behind

Harry Potter meets a stranger by the name of Marvolo while he is at Malfoy manor. Marvolo helps him gather some blackmail material to taunt Draco with when they get back to school. Voldemort is intrigued by the boy who apparently doesn't recognise the ruler of magical Britian, and wants help gathering some material to humiliate a classmate with.