Book 5 of the Wildflowers series (series numeration from Goodreads.com).

Misty, Star, Jade, and Cat first came together in Dr. Marlowe's group therapy sessions. They trusted no one but each other -- and even that bond was fragile at best. One by one, each of the Wildflowers told her own story and bravely unveiled the inner wounds inflicted by years of lies, deceit, and untold family secrets; each revealed the shocking tales of how their parents hurt them, used them, or simply abandoned them. And as they shared their darkest feelings, they no longer felt like lost souls with nowhere to turn. Finally, years of loneliness and pain gave way to the realization that someone else in this world understood them. But then the sessions ended, and the girls didn't know if they would ever see each other again. Now they are coming together one more time. Jade has sent out invitations to her parents' mansion -- the sprawling, opulent home that served as a battleground for much of her young life. There, the four will rekindle their bonds of friendship and trust. But this time, away from Dr. Marlowe's watchful eye, it will be different. Today, in the mansion's attic, Star, Jade, Cat, and Misty will take each other's hands and swear to tell the real truth -- the shattering secrets that lie deep within them like smoldering coals. And once the darkest secret of all is spoken aloud, there will be no turning back. For there may be some things the Wildflowers should leave buried forever....