SOLVED. YA Occult Mystery set in UK [s]

[Christopher]

Another mystery I'm trying to remember from middle school, early 80's. It was about a teenager who went to stay with an aunt whose name I remember was Philippa. The woman lived in an old cottage. The boy discovered a secret stairway and passage that went way underground and when he followed it he found evidence of people practicing witchcraft.

[Christopher]

I forgot to add that it was set in the UK.

[Kris]

How about Blackbriar by William Sleator? Here are some descriptions on Goodreads:

"Blackbriar is the story of Danny, a young boy from London who has lost both his parents. Now he lives with the secretary at his school, Philippa Sibley. She wants the best for him, but is also a little protective of Danny. Quite early in the story, Philippa decides to buy a house on the countryside and forces Danny to come and live with her. The house is called Blackbriar and is a haunted house. They find a strange door to the basement with some old names and dates. The last name, Mary Peachy, is the only name with a date. They also find a strange wooden figurine that Philippa dislikes, in fact, she asks Danny to take it outside. He doesn't, of course, instead he hides it in his room."

"...the spooky goings-on in an old country cottage in Britain that turns out to have connections to the Black Plague and modern-day witchcraft..."

"...the cat, Islington..."

[Christopher]

Yes, Blackbriar! Thank you!

[Kris]

You're welcome. Glad you found your book. :)

[Teresa]

Weird question: Is there an incident in Blackbriar where something like a model pterosaur becomes animate (and dangerous)? I ask because if it isn't in there, then there is a book that has mingled with Blackbriar in my mind.