YA novels, mysteries, held in school basement, bangs on pipes

I'm trying to remember the name of a small group of books for young adults, set in a high school. Each book has a different protagonist. In one novel, a character is kidnapped for some reason and held in the basement of the school. He or she bangs on the pipe and is heard in one of the classrooms and found. In another scene (perhaps in a different one of the books?) there is a big school bonfire. It was an interesting series (at least two books, possibly three) in that the protagonist changed each time, and a character featured in one book was just a person walking by in the hall in a different book.

What year was it read?

Could it be the Diane Hoh Nightmare Hall series? It's a different protaganist in each book, it takes place in a school, but some characters overlap.

@bookel: Maybe...1974?

This is "The Mysterious Schoolmaster" by Karin Anckarsvaard.

I'm sorry I posted my query and then let it lapse for so long, but yes--the more I read about the Anckarsvärd trilogy of books, the more I think it's the one. Thank you so much, Cornelia!

Thanks much for coming back and letting us know!

Touchstone add: The Mysterious Schoolmaster