The Toil and Trouble Trilogy, Book Three

Berserkers have overrun the city. Olivia, Josh, Fitzpatrick and a group of survivors hide out in a fortified apartment building they call the compound. But the atmosphere is tense. Olivia struggles to gain control over her magic, hoping to be able to use it to wipe out all the berserkers.

After her ex-boyfriend-turned-monster Brice attacks the compound with a berserker army, Olivia realizes that Brice is the most powerful berserker ever. He controls the monsters with his magic, and he's obsessed with one thing: getting revenge on Olivia.

Olivia never wanted to kill Brice, but if she doesn't, he'll destroy not only her, but the entire city