Starfall (Tower of Somnus #3)

Her allies are gone or preoccupied, forcing her and the few friends she’s made to try and root out the invaders without formal support. As her investigation heats up, revealing a situation worse than Kat ever could have expected, she needs to confront an unpleasant fact: not all of humanity's enemies are aliens.

Now Kat is racing against time, both in and out of the tower. Despite her skills, magic, and allies, her best may not be enough.