This preoccupation with the past intensified into the mid-1980s, as Grothendieck worked on the manuscript for Harvests and Sowings. A reflection on his mathematical career, it was filled with stunning aphoristic insights, like the house metaphor. But, choked with David Foster Wallace-like footnotes, it was relentless and overwhelming, too – and steeped in a sense of betrayal by his former colleagues. In the wake of his revelations about his parents, this feeling became a kind of governing principle. “It was a systematic thing with our papa – to put someone on a pedestal, in order to see their flaws. Then – bam! – they went down in flames,” says Alexandre. Although he still produced some mathematical work during this period, Grothendieck delved further into mysticism. He looked to his dreams as a conduit to the divine; he believed they were not products of his own psyche, but messages sent to him by an entity he called the Dreamer. This being was synonymous with God; as he conceived it, a kind of cosmic mother. “Like a maternal breast, the ‘grand dream’ offers us a thick and savorous milk, good to nourish and invigorate the soul,” he later wrote in The Key of Dreams, a treatise on the subject. Pierre Deligne, the brilliant pupil he accused in Harvests and Sowings of betraying him, felt his old master had lost his way. “This was not the Grothendieck I admired,” he says, on the phone from Princeton’s Institute for Advanced Study. He became totally isolated. He was no longer in contact with nature. He had cut ties with everyone By summer 1989, the prophetic dreams had intensified into daily audiences, “absorbing almost all of my time and energy”, with an angel Grothendieck called either Flora or Lucifera, depending on whether she manifested as benevolent or tormenting. She tutored him in a new cosmology, central to which was the question of suffering and evil in God’s greater scheme. He believed, for example, that the speed of light being close to, but not precisely, 300,000km a second, was evidence of Satan’s interference. “He was in a form of mystic delirium,” says another former pupil, Jean Malgoire, now a professor at Montpellier University. “Which is also a form of mental illness. It would have been good if he could have been seen by a psychiatrist at that point.” In real life, he had become forbidding and remote. Matthieu spent two months in Mormoiron working on the house; during that time, his father invited him in only once. His son blew his top: “He’d lost interest in others. I could no longer feel any authentic or sincere empathy.” But Grothendieck was still interested in people’s souls. On 26 January 1990, he sent 250 of his acquaintances – including his children – a messianic, seven-page typed epistle, entitled Letter of the Good News. He announced a date – 14 October 1996 – for the “Day of Liberation” when evil on Earth would cease, and said they had been chosen to help usher in the new era. It was “a kind of remake of the most limited aspects of Christianity”, says Johanna. skip past newsletter promotion Sign up to Inside Saturday Free weekly newsletter The only way to get a look behind the scenes of the Saturday magazine. Sign up to get the inside story from our top writers as well as all the must-read articles and columns, delivered to your inbox every weekend. Enter your email address Sign up Privacy Notice: Newsletters may contain info about charities, online ads, and content funded by outside parties. For more information see our Privacy Policy. We use Google reCaptcha to protect our website and the Google Privacy Policy and Terms of Service apply. after newsletter promotion Then in June 1990, as if to firm up his spiritual commitment, Grothendieck fasted for 45 days (he wanted to beat Christ’s 40), cooling himself in the heat of summer in a wine barrel filled with water. As he watched his father shrivel to an emaciated frame reminiscent of the Nazi concentration camp prisoners, Alexandre realised he may have been emulating someone else: “In some way, he was rejoining his father.” Grothendieck almost died. He only relented when persuaded to resume eating by Johanna’s partner. She believes the fast damaged her father’s brain on a cellular level in a way impossible for a 62-year-old to recover from, further loosening his grip on rationality. Shortly afterwards, he summoned Malgoire to Mormoiron to collect 28,000 pages of mathematical writings (now available online). He showed his student an oil drum full of ashes: the remains of a huge raft of personal papers, including his parents’ letters, he had burned. The past was immaterial, and now Grothendieck could only look ahead. One year later, without warning, he moved away from his house on a trajectory known only to him. Acircular slab of black pitted sandstone, fashioned by Johanna and now smothered in wild roses, marks Grothendieck’s resting place in Lasserre churchyard. It’s almost hidden behind a telegraph post. The mathematician was