She is one of the most written about authors of the 20th century. Sylvia Plath has inspired not only poets and poetry lovers, but also biographers keen to analyze her life and work. Many books on Plath have been published since her 1963 suicide. One was “American Isis: The Life and Art of Sylvia Plath,” which Carl Rollyson, professor emeritus of journalism at Baruch College, published in 2013 to mark the 50th anniversary of her death.

His new book, “The Last Days of Sylvia Plath,” was precipitated by a new development. As Rollyson states in his introduction, the recent discovery of many of Plath’s letters and “the partial opening of her psychiatrist’s papers … stimulated an irresistible desire to explore once again what happened to Sylvia Plath, especially what had occurred in the England of the 1960s that had done so much to forge my own identity.”

According to Rollyson, previous biographers were frustrated in their efforts by “the coercive conspiracy against their work.” led by Plath’s husband, Ted Hughes. Rollyson writes that Hughes, along with his estate, “protected a hoard of material” about Plath and that Hughes and his sister Olwyn “threatened lawsuits and conducted campaigns” against biographers and limited access to her letters.

The most notable new information here comes from the recently released papers of Ruth Tiffany Barnhouse, Plath’s therapist and the model for Dr. Nolan in Plath’s novel “The Bell Jar.” In exhaustive if sometimes dry detail, Rollyson focuses on events from Plath’s final seven months as recorded in her letters, events that seem to rebut the contention that Plath’s final days were nothing but increasing hysteria.

The Plath who emerges from these writings is as active as she had been for much of her life. Her output “would seem the opposite of depression” and “nothing so much as a general fielding her forces”: writing new poems, reviewing historical biographies, working on “potboilers” she planned to write under a pseudonym, all while caring for her two children with Hughes and dealing with the trauma of his marital infidelities.

Barnhouse’s responses to Plath’s letters are unknown, as her correspondence is missing. But Rollyson ably interprets Plath’s confessions to Barnhouse and challenges the popular notion of Plath’s decline while also noting that, as Plath admitted to Barnhouse in her final week, she feared “the return of my madness, my paralysis, my fear & vision of the worst.”

In his zeal at having uncovered these letters, Rollyson sometimes errs on the side of excess. Not every letter contains newsworthy information: invitations to friends to visit her in England, and so on. And the book would have benefited from more analysis. But admirers of Plath will likely find this a noteworthy addition to the field of Plath scholarship.

 Michael Magras is a freelance book critic. His work has appeared in the Economist, Times Literary Supplement, Pittsburgh Post-Gazette and BookPage.

The Last Days of Sylvia Plath<
By: Carl Rollyson.
Publisher: University Press of Mississippi, 235 pages, $25.