Hannah Green and Her Unfeasibly Mundane Existence by Michael Marshall Smith (Books 2019, 17)
No, it’s me, not London Below: this has also faded quickly from my mind, despite the fact that I love MMS, and I really enjoyed this as I read it.
Still, it’s very good. Hannah is an ordinary girl living in present-day California with her dad and (maybe) mum (sorry, mom).
Until the devil turns up, and her grandfather turns out to be his engineer. And he knew Bach.
Inevitably, the world needs to be saved.