A New Darkness by Joseph Delaney
A New Darkness is the first book in the Starblade Chronicles and follows Tom Ward, from the The Last Apprentice series, who is no longer an apprentice, he is now a Spook battling all of the ghosts, witches and everything else that appears in this world. But because Tom is only 17 and couldn't complete his apprenticeship because his leader was killed, nobody really trusts him. Tom must prove himself in this action-packed series-starter and he teams up with Jenny, who wants to be the first ever female Spook.
The series is three books and although it is created in Delaney's well-known world, the series can be read on its own without having read any of Delaney's other books. I would highly recommend reading this series, it's definitely a classic Delaney-style fantasy novel.