As the kettle boiled and, after that, as the tea brewed – for what Wada judged to be far too long – Joan gently interrogated her about why she – or rather Mimori Takenaga – had travelled all the way from Japan to meet Martin Caldwell. It became apparent that she regarded Caldwell as someone who occasionally needed saving from himself. It also became apparent that the theory she and her husband Wally had come up with to explain Caldwell’s rendezvous in London with a mysterious Japanese woman was some kind of internet romance.

Wada explained that romance had nothing to do with it. She’d come to see Martin Caldwell in order to shed light on the circumstances of her father’s death in London in 1977.

‘Oh, Martin knew your father, did he, dear?’ Joan asked quizzically as she finally poured the tea.

‘It’s more likely he knew someone who knew him, Mrs Stapleton.’

‘You can call me Joan, dear. Biscuit?’

‘I’m not hungry, thank you.’ Indeed she wasn’t. But she was observant. And the removal of the biscuit tin from a shelf had disturbed a key, hanging on a hook above the worktop. She was also blessed with good eyesight, which revealed there was a number written on the cardboard tag attached to the key ring. The number was 6.

‘They’re shortbreads. Delicious. I don’t suppose you can get them in Japan.’

Wada smiled, thinking of the vast selection of Scottish shortbreads she’d seen in the food hall at Takashimaya. ‘You’ve persuaded me,’ she said.

Bearing a tray, Joan headed off into the lounge. Wada debated the issue with herself for a fraction of a second, then took a sidestep to the worktop, lifted the key off the hook and slipped it into the pocket of her trousers. She removed a glove from another pocket as she did so and dropped it on the table. The plan she’d improvised was to come back later to retrieve the glove, surreptitiously returning the key at the same time.

‘Martin must have been living here in 1977,’ Joan continued, as Wada caught up with her. ‘He was a student at the university, you know. He’s told me this was quite a lively place then. It wasn’t divided into flats until later. I suppose him and his student friends lived in some kind of commune, if you know what I mean.’ She pronounced the word commune as if the concept of such an arrangement was deeply sinister. ‘Nothing like that now, I can assure you. Quiet as the … well, quiet is what it is. Which is how Wally and me like it. Martin too. You don’t want noise and carryings-on at our age, do you?’

They sat down. Wada stifled a wince as she sipped the tea. It was even stronger than she’d feared. She took a bite of shortbread. ‘When did you last see him, Joan?’