At that time, deeply committed to Greiffenhagen, Catherine embarked on what most people must have thought was a hopeless attempt to free herself from her own marriage. She could not divorce Jackson, as the law then stood; and he, being certified insane, could not divorce her. Her unprecedented case was that because of his developing mental illness he could not have fully grasped what he was undertaking when they were married, and so the marriage was null and void.

Jackson v Jackson came to court in May 1908 and lasted six days, during which Catherine gave evidence about her extraordinary honeymoon, facing strict cross-examination. Several doctors were called, one of whom, challenged on the point that he had examined Herbert Jackson only after the marriage, compared the forest tree he had seen in the disease with the sapling that must have preceded it. It was powerfully urged on Jackson’s side that a nullity would make the child illegitimate, which no court should allow – least of all on the request of the mother. Jackson himself, his counsel said, was too ill to appear. “The respondent,” said Mr Justice Bargrave Deane, “was not at the time of the marriage a raving lunatic: outwardly to people he was competent. The question is, whether he was really insane.” It was for her to prove it, and he found that she had, so establishing a leading case.

Three years later, in 1911, she received D. H. Lawrence’s first novel, The White Peacock, in her pile for the Herald, and declared that she found in it “a new voice”. Soon afterwards, on the death of her mother, she moved to London (where Greiffenhagen was now living) and established herself in a cottage in Hampstead with Diana. The dramatic criticism for the Herald naturally had to stop, but she continued to review their fiction every other Tuesday, so their columns included favourable notices of The Trespassers and, more enthusiastic still, Sons and Lovers.

It must have been about this time that she began writing the novel that became Open The Door!; her relationship with Greiffenhagen was collapsing under his resolution to follow his own path, and Donald Carswell had also taken the plunge to London with the post on The Times.

Diana, never a well child, died of pneumonia in 1913 after “eight happy years”, as her mother wrote on her grave in Hampstead churchyard. Soon afterwards Catherine and Donald became engaged, and he was to prove an utterly devoted husband – but the name of Greiffenhagen could never be mentioned between them.