I'm looking for a book that I vaguely remember

[Nightshade]

Book was fiction.
A man appears naked and injured/sick at possibly a nunnery, is nursed back to health, and I think meets a young girl. There's some sort of adventure, I believe he had an odd instrument, and music played in between chapters.
I read it (listened to it, really) around 10-12 years ago.
Young Adult Fiction.
Borrowed it from a library in Canada (BC).
The cover had a golden mirror, possibly with the man or child's silhouette, I think it was over a mantle, with green wallpaper.

If anyone knows the title or where I can find it, that would be greatly appreciated!