After years of no contact, former friends Alix, Ben, Zara, and Dean meet up at their old school to keep a longstanding promise: to open a memory box they left there when they were thirteen. But there is a gaping hole--their friend Millie has died. Secrets tumble out and old feelings rise to the surface as they dredge up the past. Can they save the friendships that once meant everything to them, or is it time to let go and say goodbye?