Any One of Us by Martyn Ford
Her old schoolfriends are dead. She might be next. When Ruby hears from her best friend Elizabeth that two of their old classmates have been murdered, Ruby is more certain than ever that leaving her hometown was the right decision. But after Elizabeth suddenly stops responding to texts, and Ruby hears a third classmate has been killed, she knows in her heart what has happened. Elizabeth is dead too. Missbrook Bay is a place haunted by memories Ruby wanted to forget, and people she never wanted to see again, but Ruby has no choice but to go back to investigate. While staying with her ex-boyfriend, she notices a pattern in their full school year photo-the killer seems to be working through victims in a specific order. And after her ex's house is broken into, Ruby realises nowhere and no one is safe. There are still many faces left in that photo. Any one of them could be the next victim-and any one of them could be the killer. And with each death, the killer is getting closer to Ruby.