The Vow of Secrecy is a pledge taken by every witch or wizard upon coming of age which prevents them from revealing any information regarding the existence of Hogwarts to any Muggle individual or agency by a variety of jinxes or curses. The parents of Muggle-born students sign a similar non-disclosure promise.

Ralph Deedle's father was affected by neither. He was sent to live among the Muggles before becoming of age, thus he never took the Vow of Secrecy and, as he is a Squib and not a Muggle, he was not bound by the Muggle Non-disclosure Contract. This makes it possible for him to lead Martin J. Prescott’s crew onto the castle grounds.