In the spring of 1967, Mary Theresa Brunner embarks on a life-altering journey as she leaves her quiet Midwestern town behind to embrace the vibrant energy of San Francisco's revolutionary atmosphere. As an assistant librarian at UC Berkeley, Mary finds herself at the heart of the Peace/Love movement, surrounded by activists and dreamers seeking a better world.

The First Manson Girl is a captivating tale that follows Mary's path of self-discovery and rebellion against the expectations of her conservative upbringing. With the backdrop of an era defined by social change and countercultural movements, Mary's quiet demeanor belies the profound impact she will have on those around her.

As Mary navigates the tumultuous landscape of the late 1960s, she becomes entangled in a web of love, friendship, and radical ideologies. Along her journey, she encounters figures who will leave an indelible mark on her life, including the enigmatic and magnetic Charles Manson.