Book about a demon and spooky stuff investigator with a musical instrument

Question

I've been thinking of a series of books I read when I was a teenager and I'd like to find them again!

It's about a guy who captures demons with a flute or a pipe, something like a wind instrument.

I remember he started off in college with his best friend trying to summon a demon and it of course goes wrong... he ends up joining the demon and the soul of his best friend together and this best friend pops up in the books as a great character sometimes.

I remember in one of the books the lead guy has his jaw ripped off by a demon and can't play his flute anymore, I think they are in a stairwell.

I remember it was a cool set of stories.

I think in one book (not sure if I'm blending books together now) he is hired to investigate a haunting of a museum or library where rare books are kept. Everyone thinks the place is being haunted by a nun with a red veil, turns out it's a woman that was killed by the janitor by punching her in the face whilst holding a set of keys and that's why her face is red when she's seen in the building. I remember they plot out all the sightings of her and it's like she's tied on a string to the basement apartment.

Answer 1

I think this is the Felix Castor series by Mike Carey.

In the first book Felix does use a flute, and his friend Rafi is possessed by Asmodeus. The ghost with the red veil appears in the first book as well, however it is not a nun:

I turned the glass in my hand, watched the facets catch the light. "Ghost takes the form of a young woman with most of her face hidden behind a red veil. Multiple sightings, persistent over time – about three months, give or take – but spread out over the building so there’s no locus where I can easily read her from."

Felix discovers the ghost is a Russian girl who was assaulted and murdered:

But when I turned to number three, I knew I’d found my ghost. Unlike the other two, she didn’t have a name: just a case number and a clinical description. One hundred and fifty-nine centimetres in height; hair brunette; eyes brown; build slender; age approximately mid-twenties. Naked, but a T-shirt found near the body provided samples of her blood and sloughed skin cells when tested. She’d been found in a skip on a builder’s yard in the hinterland beyond the Ampthill estate, dead for at least three days. The date on the incident report was Wednesday, 14 September – the day after the ghost was first sighted at the Bonnington archive.

I don't recall Felix getting his jaw ripped off in any of the five books.