Agnes and her aunts were huddled at the kitchen table below a ceiling across which yellow stains sailed in cloud formations, surrounded by a litter of saucepans and the unopened cans of soup on which the aunts appeared to survive. The cold crept round their feet and an acrid underlying whiff of mould emanating from the leaking window seemed more than usually noticeable.

Agnes drank her tea out of the thick white cup that had once been of use in a station canteen before fetching up in a jumble sale. It tasted dead, if such a thing were possible, and her stomach protested. Grief was a funny thing, circling round like a tiger and pouncing just at the moment you thought you had it under control. Guilt, as she knew from experience, did not bother with the circling.

At any minute now, she must spring into action. With some amusement, she had read about how families assign roles to the separate members – the moneymaker, the fool, the dreamer – and now Agnes had been assigned hers. That was fine. That was what was expected of her, and what Agnes expected of herself. She knew, and they knew, that despite their sparring the sisters were united in their expectation that Agnes would take charge of both the argument and of the future. Agnes will know what to do.

‘I had to tell John the truth. I was taught to tell the truth.’ Maud raised her eyes to the ceiling and dropped them again when she encountered the colony of spiders in the cornice. She faced Agnes. ‘You weren’t the only one in his life,’ she said, dripping bitterness. ‘I was the one who was married to him, you know.’

Bea was apparently fixated by the dingy laurel tree that guarded the entrance to the kitchen yard. ‘It wasn’t kind, Maud.’ She did not look at her sister. ‘You must have peace when you’re dying.’

Agnes braced herself. ‘What did you say, Maud, that was so terrible?’

Maud’s bulldog expression said: You can’t shame me. ‘That I was sick and tired of words like “heritage”, and how ridiculous it had been that because he was the owner of a house like this we had been martyred all our lives to it. What’s more, I told him I wanted to move out and live in a bungalow. A nice warm modern one. There, that’s what I said.’

Agnes stared at Maud. In a normal marriage one hoped for a little peace in which to shelter. Pierre had agreed, adding that his marriage to Madeleine did not stop him worshipping Agnes’s size seven English feet and long ash-blonde hair. As a result, a besotted Agnes in all innocence, no, foolishness, had spent four years imagining that Pierre would leave his wife in the flat on the rue Jacob in Paris with the three elfin daughters.

She knew those daughters as well as she might have known her own, for everywhere she went, in everything she did, they were there, like the tender, infant putti in the paintings: Katrine, the clever one, Claudine, the pretty one, and Mazarine, the plump little angel of the family. She had been jealous of them, the only considerations that gave Pierre pause. Their innocence, their physicality, their needs were balanced in the palms of Pierre’s hands, and Agnes hated it, and hated herself for that.

That was before Madeleine had arrived at Agnes’s hotel one evening and pointed out how terribly the family was suffering, and if Pierre said otherwise he was lying. After that, everything changed, and because Pierre was forbidden, Agnes wanted him even more. Yet the more she wanted him, the more she thought of Madeleine until, in some tortured fashion, Madeleine became more important, the one who occupied Agnes’s thoughts.

After she had told Pierre it was over and that she was not coming back to Paris, Agnes had finally tumbled to the conclusion that the good and bad areas of a marriage were irrelevant. You grew round the other person, like fat and muscles over organs, and that was that.

Maud shrugged. ‘You needn’t look so disapproving, Agnes. I have a point, and John knew it. Anyway, he probably didn’t hear what I said.’

‘But he did.’ Bea was as fierce as it was possible to be.

No fool, Maud realized that her trespass was too far and she adjusted her tone to a more reasonable one. ‘You ought to sell this millstone, Agnes. It’s done nothing but bring trouble and misery on all of us. Think. We could all have some money to buy somewhere sensible.’

Agnes’s fingers folded across the cup and tightened but she said nothing. An empty bag is impossible to burst and it was best with Maud in this mood to be as empty as possible.

‘For a start, there’s a leak in the blue bedroom ceiling,’ said Maud, ‘and the roof is getting worse.’

‘I know, I know,’ said Agnes. Maud had a nose for the details. ‘It’s on the list.’

‘Long ago,’ Maud had once, in a rare soft moment, told the frightened little cuckoo who had dropped into her nest, ‘John and I had to mend the roof. Nail fatigue, I think. The men found a plate in the rafters, one of the Delfts. A maid must have broken it and been too frightened to own up. She would have lost her place.’

That a plate could so alter a life had shocked Agnes. She had asked to see the pieces, and Maud obliged. Agnes cradled them in her hands: indigo blue and greyish white shapes, which had ridden over a dark sea from Holland to the sun-flecked drawing room in England. If she thought hard enough, she could still feel the sharp, gritty edges that had grazed her skin.

‘But why ever not sell?’ Maud saw the nice, clean, warm bungalow slipping away.

Agnes finished her tea. As clearly as if he was in the room, she heard her uncle’s voice. ‘Family, tradition, history, not letting go…’ Those were the charges laid on her by him. To be fair to Maud, they probably did not make sense. But they made absolute sense to Agnes. ‘By the way,’ she said, ‘the Jane Austens are missing from his bedroom. Someone has moved them. Do you know where they are?’

‘You were wrong,’ said Bea, for a second time. She whirled round, fierce and trembling.

Maud poured herself another cup of tea. ‘Thank God I’m not a proper Campion,’ she said. ‘It’s perfectly ridiculous.’

Both Agnes and Bea knew exactly what this outburst betokened. Maud had always felt excluded, an interloper of forty-five years who could never quite see her way into the charmed circle. The pretty bride who had married John had never truly found her niche.

‘Actually, can we not argue?’ Bea looked ill with distress.

Agnes reached for her bag and extracted her notebook. ‘Let’s sort a few things out, then we can have lunch.’

‘I’ll lay up.’ Bea struggled to her feet.

Maud watched her sister bustling around with china and silver. ‘Not those spoons for soup, Bea,’ she said, after a moment or two. ‘Will you never learn?’

A couple of hours later, Agnes tucked Bea into bed for a nap and ordered her to stay put for at least an hour. Maud retired to the small sitting room, formerly the butler’s pantry, in which the television and video-recorder were installed. Within minutes, music drifted through the house.

Tackling a pile of paperwork in her uncle’s study, Agnes heard the familiar notes and knew exactly what Maud was watching. First, the unsoiled grey-green vista of an Alpine mountainside on which a dot appeared to fling wide its arm and loose a string of high notes. Then, in a director’s sleight of hand, the camera panned down to transform the dot into Julie Andrews. Once again, Maud was worshipping at the shrine of The Sound of Music.

Agnes gritted her teeth and telephoned Bel, her co-director at Five Star, the production company they ran together. Bel operated from the London end and they kept in constant touch. Half-way through their discussion on the schedule for their project, The Death of the English Apple, she heard Maud cry out. Agnes shot down the passage to find her transfixed in front of the screen, which was now a mass of moving colour and song.

‘It’s so sad. I can’t bear it.’ Maud pressed a hand to her mouth.

Agnes sat down beside her. ‘Maud, John was eighty. I know he didn’t want to die but perhaps…’ She could not bring herself to continue.

Maud stiffened. ‘Oh, that,’ she said. ‘I meant,’ she pointed to the screen, ‘she looks so young and beautiful, so pure, and I can’t bear it.’

Agnes looked. Julie Andrews was progressing up the aisle in her wedding dress, and the choir were singing like angels. She counted to five and leaned over to tuck the tartan rug around Maud’s angular form. ‘You know this is your home, don’t you? Always. You mustn’t worry.’

Maud dropped her hand and turned a countenance on Agnes on which incomprehension and anger were etched. (Agnes could almost predict the number of seconds required for Maud to slot into dramatic gear.) But Maud surprised her. She stretched out an arm to Agnes, the paste ring quivering on her finger like a roosting insect, and the aggression was replaced by a weary regret. She pulled at a fold of papery skin at her wrist. ‘Look at me. Old. Drained. Fatiguée. If you take on this house, you will end up the same.’

‘Hush, Maud.’ Agnes tried to soothe her, but Maud grabbed her.

Believe me.’

1939-45 was the era of yet another war, and of Morse code.

Before sending a message from the field to Home Station, an agent was required to key a message into a numbered phase. From there, he or she would hook it up to a second transposition, at which point the original message had been thoroughly scrambled.

The concept of double transposition appealed to Julian Knox, who, being fascinated by codes, had picked up a history of the Special Operations Executive during the Second World War in a bookshop and bought it. He had reached the section on coding. The mathematical constructions were fascinating. So was the neatness of a code and, in contrast, its risky fireworks and the dig-deep analysis to which he responded. He liked, too, the exhilaration of stalking an objective enfolded in cryptographic darkness and of dragging it into the light. He liked the puzzle and, when the key was exposed, its absolute rationality.