Darkness Brutal, by Rachel Marks

It turns out that this is a young adult book. (Amazon has it listed in both the "teens" and "romance" categories; had I known that ahead of time I'd probably have avoided this even though it was available for free. I guess that will teach me not to jump to conclusions.) Anyway, the YA category does explain a bit about why all the lead characters are teens and why some of their decisions are, well, the kind of decisions that teens make.

The hero is Aidan, who sees demons. Orphaned, he strives to protect his younger sister Ava who is in a foster setting while he lives on the street. It turns out his abilities are significant and the usual mayhem ensues.

I don't read much of the para-normal genre, but it seems to me unusual to find a lead character burnishing a Star of David to ward off a demon. So that was pretty cool.

There were some annoying aspects of the book, but overall it was quite interesting - enough so that I do intend to read the sequel, even if I can't get it for free.

Darkness Brutal (The Dark Cycle Book 1)