During the six-year marriage, Plath won a contract with The New Yorker and published her first collection, “The Colossus and Other Poems.” The pair separated after Plath discovered Hughes’s affair with Wevill, who was also married. In the last months of her life, while caring for their children, Frieda and Nicholas, in a freezing London flat, Plath ricocheted back and forth between trying to win Hughes back and ordering him to disappear.

In Rollyson’s account, her depression likely deepened when Al Alvarez, a close friend and influential poetry critic, rebuffed Plath’s sexual advances. In support of that hypothesis, he cites a letter by Olwyn Hughes to Alvarez referencing a revealing entry about Alvarez in a Plath journal that Ted Hughes had described as “lost.” Alvarez told Rollyson that he believed Plath had been in love with him.

Rollyson also, somewhat romantically, accords the poetic impulse some blame for the suicide. “The energy Sylvia expended in the early morning writing sessions stripped her of the power to deal with the rest of her day,” he argues.

What is inarguable is that the extreme imagery of Plath’s “Ariel” poems — in which her poetic double can “eat men like air” and flies “Into the red/Eye, the cauldron of morning” — repelled critics at first and later, as she had predicted, made her name. They conjure a woman in the fierce grip of emotions that she can control only on the page.

It is interesting to compare how differently Rollyson and Wilson treat two incidents. The first, fictionalized in Plath’s sole published novel, “The Bell Jar,” is her interaction with a sexually predatory mathematics professor. After a first date, Plath hemorrhaged so much blood that she had to be hospitalized. By way of explanation, she told her Smith roommate that she had been raped. But when Plath recovered, she inexplicably continued the relationship.

Rollyson, generally more sympathetic to Plath, believes the rape story, while calling her subsequent involvement with the professor “reckless.” Wilson theorizes that Plath may have welcomed the sex, if not its bloody aftermath, “as a way of expanding her erotic repertoire.’’

Also at issue is the rejection Plath received in 1953 from Frank O’Connor, who did not admit her to a creative writing class he was teaching at Harvard’s summer school. In part because no letter exists in Aurelia Plath’s meticulous archives, Wilson speculates that the ailing Aurelia might have invented the rejection to keep Plath home that summer. But Rollyson, without citing a source, says that O’Connor has confirmed rejecting Plath — but only because he believed her already “too advanced for his class.” If only the self-doubting Plath, who hurtled into her first suicidal depression shortly afterward, had known that — yet another “if only” to haunt her acolytes.

AMERICAN ISIS: The Life and Art of Sylvia Plath

By Carl Rollyson

St. Martin’s, 319 pp., illustrated, $29.99

MAD GIRL’S LOVE SONG: Sylvia Plath and Life Before Ted

By Andrew Wilson

Scribner, 368 pp., illustrated, $30