Rollyson is the first biographer to gain access to the papers of Ruth Tiffany Barnhouse at Smith College, a key figure in the poet's final days. Barnhouse was a therapist who may have been the only person to whom Plath believed she could reveal her whole self. Barnhouse went beyond the protocols of her profession, serving more as Plath's ally, seeking a way out of the imprisoning charisma of Ted Hughes and friends he counted on to support a regime of antipathy against her.

The Last Days of Sylvia Plath focuses on the train of events that plagued Plath's last seven months when she tried to recover her own life in the midst of Hughes's alternating threats and reassurances. In a siege-like atmosphere a tormented Plath continued to write, reach out to friends, and care for her two children. Why Barnhouse seemed, in Hughes's malign view, his wife's undoing, and how biographers, Hughes, and his cohort parsed the events that led to the poet's death, form the charged and contentious story this book has to tell.