To Trevor Thomas, Sylvia complained about her incarceration in a flat with two children, while Ted was free to enjoy his affair with Assia and travel. Thomas tried to console her, and she said he reminded her of her father. Thomas never knew which Sylvia he would encounter: charming, stylish, distracted, or even downright rude. By late January, the lightning shifts in Sylvia’s moods accelerated. Between 28 January and 4 February, she managed to write ten poems, a surprising revival after such an appalling month. But she seemed to be turning in on herself: “People or stars / Regard me sadly, I disappoint them” (“Sheep in Fog”). Similar expressions in “Totem,” “Paralytic,” and “Mystic” constitute terse expressions of futility, relieved only briefly by poems like “Child,” “Kindness,” and “Balloons,” which show she could still take great joy in her children. “Contusion,” completed on 4 February, ends with the portentous line: “The mirrors are sheeted.” The sense of closing up, of not seeing oneself reflected in the hopes of others, and the covering of objects in rooms no longer used—as if after a death—is pervasive.

On Sunday, 3 February, Sylvia called Ted and invited him to lunch. His diary notes, written the week after Sylvia’s death, record that he remained with her until 2 a.m. They had not enjoyed such a good time since July, he remarked, as he listened to her read her new poems. Sylvia seemed to have regained her equilibrium, although she wept when he played with Frieda and embraced both of them. When Sylvia repeated her conviction that he was looking for someone else, he “kept denying it absolutely.” He wanted to return to the marriage, but on terms that would no longer include what he deemed his slavish devotion to her. He was beginning to feel like his own man again.

The next day, according to Ted’s diary, Sylvia rang him from a public call box in bitterly cold weather and demanded that he promise to leave England in two weeks. She could not work so long as she had to hear about him. Ted demanded to know who was talking about him. She would not say. And he was startled to see how the calm Sylvia of the day before had given way to this distressed woman. Even when he said he could not afford to leave England and had no place he wanted to go, she extracted his reluctant agreement to depart the country. “She wanted me never to see her again,” Ted wrote. He talked over her phone call with Al Alvarez, who described his own divorce and regret that he had continued to see his wife after they were irreconcilable. Alvarez advised him to do as Sylvia said. Ted decided he would leave as soon as he could.

The same day, Sylvia wrote her last, disconsolate letter to her mother, confessing, “I just haven’t written anybody because I have been feeling a bit grim—the upheaval over, I am seeing the finality of it all, and being catapulted from the cowlike happiness of maternity into loneliness and grim problems is no fun.” She saw no way out: “I have absolutely no desire ever to return to America. Not now, anyway.” Work for the BBC and other outlets had no equivalent in the United States. Aurelia’s idea to take the children for a while seemed only disruptive to her daughter, likely to upset Frieda who was so close to her father, who visited once a week. Sylvia also counted on the National Health Service. She simply did not see how she could support herself back home. “I shall simply have to fight it out on my own over here,” she insisted. A new, flighty, and persnickety German au pair bedeviled Sylvia, but still gave her some peaceful mornings and a few free evenings. This letter strained to mitigate the bad news. It is a crushing final testament because, in effect, Sylvia was saying that all of it now depended on her. Aurelia was right to think that her daughter had put up a gallant effort.

Sylvia’s last two poems, “Balloons” and “Edge,” completed on Tuesday, 5 February, perfectly express the plight of someone who seemed poised between life and death—between the airy buoyancy of the balloons her children played with, a world of wish fulfillment, and the finality of “Edge,” in which the inevitability of death is articulated with profound satisfaction. “Balloons” ends with a burst balloon, “A red / Shred” in the child’s “little fist.” “Edge” expresses a bitter but nevertheless peaceful acceptance: “We have come so far, it is over.” Was it over? In the end, Sylvia Plath gave herself less than a week to decide. It is a common pattern in suicide, these swings between euphoria and despair. The energy Sylvia expended in her early morning writing sessions stripped her of the power to deal with the rest of her day. Writing can become a regular part of an insomniac’s routine, but waking up from a drugged sleep at 4:00 a.m. every day inevitably weakens an already vulnerable constitution. How much life can be left after writing so intensely?

Like Marilyn Monroe coming to a similar endpoint, Plath’s displays of herself became more extreme. Sylvia could not root herself in her London flat, anymore than Marilyn could anchor herself while furnishing her new Hollywood home. They share the same inability to maintain a new life, while obsessing about the failure of the old one. Sylvia wrote hyperbolically to Marcia Brown, her college roommate: “Everything has blown and bubbled and warped and split.” She felt “in limbo between the old world and the very uncertain and grim new.”

Friends coped with multiple Sylvias and Marilyns, confident and full of doubt, happy and horribly angry. These women weighed upon themselves. Like Marilyn, Sylvia was entering her middle years, which are, in Leslie Farber’s words, the “most vulnerable to the claims of this sickness of spirit, which now radically questions all we have been, at the same time scorning the solace formerly sought in the future, making who we are to become the most oppressive of questions.”

William Styron has eloquently described the unremitting pain of depression that led to his own suicidal period, an agony that Leslie Farber has succinctly articulated in his writings about the suicide who feels that “one is a body one is mortal, and since, by definition, mortality is crumbling, its claims are imperious.” In Sylvia’s case, as in the life of many suicides, a terrible isolation enclosed her every move. She complained of having no friends, even though the facts demonstrate otherwise. She felt alone—as Styron did even when receiving an international award for his work. And just as his medication (Halcion) may have contributed to his depression, so the drugs prescribed for Plath may have hastened the onset of her dark thoughts. Even today, the pharmaceuticals used to treat depression have widely varying impacts on different individuals. It can take weeks—sometimes months—to find the right dose, and for some individuals that dose is never adequate.

Nothing changed in Sylvia Plath’s last week of life, and perhaps that is what bothered her, the dread that nothing would change. On Wednesday, 6 February, still angry that Sylvia’s friends were spreading tales about his ill treatment of her, Ted wrote her a note and visited her, announcing that he was going to engage a solicitor to stop the lies. She implored him not to do that. She was very upset, but not more so than on previous occasions, he vouchsafed to his diary. But she kept asking him if he had faith in her, and that seemed “new & odd.”

On Thursday, another phone conversation between them settled nothing. Sylvia briefly entertained the idea of a reconciliation, but then reverted to her demand that Ted leave the country. Her mood, however, seemed better to him. That same day, she sacked her au pair—why is not clear, although one version has Sylvia discovering the woman in bed with a man. Sylvia became so distraught that she actually struck the woman. By 8 February, her trusted Dr. Horder concluded that the drugs were not working and made plans to hospitalize her. She could not have had a more sympathetic or understanding physician. Horder himself suffered periodically from depression. Without other help at hand, Sylvia phoned her friend, the writer Jillian Becker, and asked if she and the children could come over.