Lady Midnight

Emma Carstairs and Julian Blackthorn are Shadowhunters, a race who monitor and control all supernatural beings on Earth. Furthermore, they are parabatai, which means they have been magically united in order to protect and help one another. This also means it is illegal for them to fall in love, and that is becoming a big problem.

As Emma searches for her parents' killer and Julian grapples with the return of his kidnapped older brother, they are dragged into a dangerous investigation that could destroy everything they love.

Cassandra Clare's Mortal Instruments series was wildly successful and The Dark Artifices looks likely to follow suit. Strong, angry Emma is driven by her need for revenge, while Julian silently takes on the burden of raising his younger siblings and keeping what remains of his shattered family together. They make excellent star-crossed lovers.

You don't have to have read the previous books to enjoy this one, but it would probably help.