I love so many things about it, and I really admire how ambitious it is. If it just didn't do that one thing in the ending, I could unequivocally say that I loved it, but that thing just makes me completely recoil in horror.

Tam Lin and Thomas the Rhymer — the folk tales — are pretty messed up, dark and creepy, so the book certainly is no darker than its source material. I don't mind dark children's fiction (and I don't think it's something that children need to be protected from; I think they need interested and engaged parents/caregivers who give them a sense of safety so that the children feel comfortable discussing things that unnerved them in fiction with their parents, should they require it), and my issues with the book don't really lie in its darkness. It's just never going to work for me, and I'm glad to have confirmed that on the reread.