The Secret House

There actually were five houses. Ravenclaw, Slytherin, Hufflepuff, Gryffindor and Sparrowflight. The house was forgotten because the other for house founder believed the founder was not fit to create their house, After 4 years of the house running Serenity Sparrowflight was demeaned insane by her fellow piers And the four fouder even believed all the kids sorted into this house are just like Serenity. It was the only thing all four could agree on. The four founder submerged the common room below the school securing all the students from the house in it along with Serenity. The founders placed a spell to never let them age in hope they'd be able to "sane" Serenity and themselves. They wiped the memory of all the staff. students even family members about Sparrowflight.

One night Albus and Scorpius were wondering around and found the opening and stumble in find the original common room. Serenity tells the boys what happened to her and the children and there's a way for them to help them escape that there's an object the four founders used and mostly likely hid that can break the spell and let them all out. The boys decided to not tell any adults but bring their friends to prove to their parents they are just as spectacular as they were but Serenity didn't tell them one thing. This one thing put they whole school in grave danger.

(There is x-reader character in this you're going to be one of the kids from Sparrowflight)