"Koestler's relations with women have been a source of controversy. David Cesarani alleged in his biography of Koestler, published in 1998, that Koestler had been a serial rapist, citing the case of the British feminist writer Jill Craigie, who said that she had been one of his victims in 1951.
Koestler was a domineering man. But he attracted women and many remained close friends after they had slept with him. It is implausible to write them all off as masochists, as Cesarani effectively does. Some broke with him; but then so did many other friends and acquaintances." Similarly, John Banville, in the London Review of Books, wrote: "Koestler himself, and at least one Hungarian friend, saw nothing odd in (Koestler's) bed-hopping. ‘In Central Europe,’ George Mikes wrote in defence of Koestler, ‘every woman was regarded as fair game. She could always say “no” and ... her no would be taken for an answer, even if grudgingly.’ Cesarani will have none of this political incorrectness, and stoutly declares: ‘There is evidence that as well as his consistent violence against women Koestler was a serial rapist.’ Phew. The evidence that Cesarani adduces in support of this accusation, and it is damning, is an account of a strange and shocking encounter between Koestler and Jill Craigie, the wife of Michael Foot."
Cesarani and others claim that Koestler had misogynistic tendencies. He engaged in numerous sexual affairs and generally treated the women in his life badly. In his autobiography, The Invisible Writing, Koestler admits to having denounced Nadezhda Smirnova, with whom he was having a relationship, to the Soviet secret police.