Wicked Games by Emma Dean

A killer is on the loose at the University of Morgana. Mika has to figure out who. and fast before she loses someone she cares about.
Mika’s first semester at Morgana hasn’t been going well. She nearly killed the boy she likes, and found out she has a rare specialty that will put her life at risk if anyone finds out what it is. Not only is her basic magic still blocked, but she managed to stumble across a sacrificial killing in the forest.
Finding out who killed the student and why is the only way she can keep her friends safe. Ethan, Lucien, Audrey, and a surprising addition agree to help her find out the killer and what they’re up to.
But none of them had any idea what was lurking under the school, or what the search would force them to discover.