Concord Floral by Jordan Tannahill

Concord Floral is a one-million-square-foot abandoned greenhouse and a refuge for neighbourhood kids; a place all to themselves in which to dream, dare, and come of age. But hidden there is a secret no one wants to confront, and when two friends stumble upon it they set off an unstoppable chain of events, from shadows in parking lots to phone calls from the grave. It's time for the teens of Concord Floral to start talking.