All Grown Up by Jordan Silver

Cassie has finally grown up, and Alex is on his way back to Cali from college to celebrate with his girl. He’s surprised when he gets there to realize that she’s been hiding things from him during their daily phone calls. He whisks her away to the island where they first professed their love for each other while back on the mainland; Mandy’s been wreaking havoc from her jail cell. Now the guys are scrambling to come up with ways to deal with her, never suspecting that help will come from somewhere unexpected.