Half an hour later Helen Alpert accompanied her client to the door, where, both eager to admit how they would miss one another, they said goodbye. While Anna walked swiftly up Chiswick Mall towards Hammersmith without looking back, Helen crossed the road and leaned on the river wall. It was a sunny morning, but the air had an edge: September, accepting that the game was up. The Thames ran low, with a sullenness that suggested the tide was on the turn. Two or three mallards, who had looked as if they were going to make a morning of it, honking and squabbling in the mud, suddenly took off and swept west, gaining height until they vanished behind the trees on the far bank.

Back inside, she put the Waterman file away; then changed her mind and, leafing through it angrily, began to make a fresh set of notes. The client, her personality frozen in adolescence, had disguised herself as an adult for the duration of her marriage to Tim Waterman. To what end? She had effectively erased the abjection of her life with her first husband, yet remained bound to it, and through it to the unthought known. Why allow the disguise to fall away now? As to the significance of the repeating dream: other dreams seemed as diagnostically valuable, and moreover came with all the necessary tools for their own decoding. The central problem, of course, was Michael Kearney. Helen Alpert couldn’t imagine being unable to forget a man whilst at the same time being unable to remember him. Anna’s self-deception seemed to have spread itself, deft and obdurate, into the real world: the very sparseness of Kearney’s biography – mathematician, suicide, patch of fog in every life he touched – gave him an unfocused quality.

Today, however, the doctor found herself more interested in Brian Tate, who – casting himself as the assistant, the unassuming experimentalist, workhorse to his friend’s conceptual genius – had committed career suicide so as not be left out of the grand finale of Kearney’s psychodrama. The great difference between the two men was this: Dr Alpert knew enough about Tate’s subsequent life to find him. She even had an address, somewhere deep in gentle Walthamstow, cocoon of the North London academic mafia. The file remained on her desk all morning. She took it with her to her favourite restaurant, Le Vacherin at Acton Green, where she read it again while lunch ran through its rewarding, quietly inevitable cycle – duck egg cocotte to assiette of hare to prune and Armagnac tart – and the tables emptied around her. ‘Do you know,’ she told her waitress, looking up in surprise to find it was already two in the afternoon, ‘I think I’d like the bill.’