In office, both men would be bound by the same constraints, both pinned down by the same facts, by advisors from the same graduate colleges, schooled in like-minded orthodoxies – Beard had little interest in the detail. It could make no significant difference to the world at large, was his considered opinion as he rolled through Swiss Cottage, if Bush rather than Gore, Tweedledum rather than Tweedledee, was president for the first four or eight years of the twenty-first century.

The previous afternoon and evening with the scotch had bequeathed a reckless clarity, as well as a pleasant sensation of invincibility. Now he saw that he had been taking matters too seriously. Unfaithful wife? Then get another! Cricklewood had a hung-over, pacified look with few pedestrians about, and the Sunday-morning tranquillity reminded him that his mission was simply to appease his curiosity. He had a right to know where Patrice spent half her week and how his adversary lived. A mile further on, through a sequence of side turns, Tarpin’s road turned out to be a four-lane urban motorway a mile long, connecting two arterial routes, a provisional, accidental place where the houses, pre-war semis, had an embattled, windswept look. He parked in a lay-by right outside the drive and stared at the place he had seen in the photograph, at the slats of dark-stained pine bolted to the front elevations to create a sixteenth-century look, at the motor boat slumped uncomfortably on its trailer – it could have been a rowing boat hiding under the wind-shredded plastic cover – at the coach lamp on a black post by the front door, which was in the Georgian style, and, a bold recent addition, lying on its side on the concrete, surrounded by neatly weeded beds, a red phone box. Between the near-black timbers, the house was painted brilliant white, the floral curtains behind the leaded panes were trimly ruched and drawn open.

Beard had no strong views on interior or exterior design, no prejudices against garden coach lamps and the like, and the attempt to give a nineteen-thirties suburban house an Elizabethan appearance seemed to him innocently patriotic. If he had not loathed Rodney Tarpin, he would have thought that the place suggested decency, hard work, simple-minded optimism. He knew from conversations way back that Mrs Tarpin had left last year with the three children and was living with a Welsh quantity surveyor on the Costa Brava, so there was some pathos too in the way Rodney was keeping the place up. But this was where Patrice came regularly to be fucked, and every detail, even the little wishing well and the posse of dwarfs clustered by its handle, seemed hostile. He hated them in return. Was Tarpin going to erect the phone box in Patrice’s honour? He could hear her pretending to like it. Darling, that’s so original, so creative… Enough! He got out of the car.

Because his wife had been up this way so many times before him, and because he had once been Tarpin’s employer, Beard felt entitled and at ease as he went up the drive. From one of the black gloss-painted down-pipes came the tinkle of falling water, and from the drain at its base steam rose into the November air. The master of the house was at his ablutions, rinsing from his body the DNA of Mrs Beard. The front door with its Palladian portico had an unused look, so Beard followed a narrow concrete path squeezed between the house and a wooden boundary fence that led to a side door and continued through an open gate into the back garden. He remembered Tarpin boasting of a hot tub and he wanted to see. She may or may not have been in it, but he was in the mood to be thorough, he needed to know everything.

A treeless patch of unmown lawn was separated on three sides from the neighbours by a chain-link fence just beyond which a pylon stood astride the cluttered land that lay between the houses, and he could hear the homely crackle of the power lines. Electrons – so durable, so fundamental. He had spent much of his youth thinking about them. At the age of twenty-one he had read in wonder the Dirac Equation of 1928 in its full form, predicting the spin of an electron. A thing of pure beauty, that equation, one of the greatest intellectual feats ever performed, correctly demanding of nature the existence of antiparticles and placing before the young reader the wide horizons of the ‘Dirac sea’. That was when he was a scientist, and now he was a bureaucrat and never thought about electrons. In the mid nineties he had stood with a small crowd in Westminster Abbey while Stephen Hawking delivered a speech in front of the memorial carved in stone, the exquisitely succinct form of the equation – iγ.δψ = mψ – and Beard had, for the final time, felt a stirring of the old excitement. All gone now.

Closer to the house was a square of hard standing where a rusting clothes tree stood, and bits of a fridge, and stacked white plastic garden furniture, and there it was, right by the stack, a large hardwood box, eight feet by eight, with padlocked lid supporting a coil of black hosepipe. He was relieved that this tub was not the Californian dream he had unconsciously assumed – no sequoias, no cicadas, no Sierra Nevada. But when he walked back towards the side door he remained unhappy, for now it was confirmed – it could only be the sex. What else would bring her to this dingy patch? But then, in his condition, was it not unhappiness that he was looking for?

At that thought he heard a sound above him and, looking up, saw on the first floor a steamed-up steel-framed window swing open, then Rodney Tarpin’s pink, wet face.

‘Oi!’

Abruptly, the face disappeared, and the window remained open, allowing shower steam to billow out, and from inside the house came a muffled sound of bare feet pounding at speed down carpeted stairs. As Beard waited by the side door, arms folded against his chest, he had no plan, he had no idea what he wanted to say. He had spent too much time brooding, waiting, and now he wanted something to happen. It hardly mattered what it was.

Two bolts were drawn back, the aluminium handle shot down, the door flew inwards and his wife’s lover stood before him on the threshold.

Beard thought it important to speak first. ‘Mr Tarpin. Good morning.’

‘What the fuck do you want?’ The stress in his query was on the ‘you’. He wore a not very large red towel tucked around his considerable waist. Water droplets trickled from his head onto his shoulders and meandered down through his chest hair in the zigzag movements of a pinball.

‘I thought I’d come and have a look round.’

‘Oh yeah? So you just walk in here.’

‘My wife does.’

Tarpin seemed put out at the directness of this reference, as though he thought it unfair, or going a little too far. Still faintly steaming, he stepped out onto the path, apparently oblivious to the cold – two degrees centigrade, according to the digital display in the car. Beard was standing seven or eight feet back, arms still crossed, five feet six in his boots, and did not give way when Tarpin planted himself right in front of him. Even barefoot, he was a big fellow, certainly strong above the waist, but thin-shanked below it – a builder’s build – and also flabby across the chest, recent fat smeared over muscle, with a beer and junk-food gut whose lateral extension far exceeded Beard’s own. That towel was hanging by a thread. What was Patrice doing with such a man if not seeking the perfection, the ideal, of her husband’s form? Tarpin’s face was a curiosity. It had a ratty look, not entirely without charm, but it was too small for the head. A small man’s whiskery, inquisitive features had been sunk or projected onto a space they could not fill. Tarpin peeped out from his own skull as though he was wearing an outsized chador. Since Beard had last seen him, the builder had lost a tooth, an upper incisor. Beard was disappointed not to see a tattoo, a snake or motorbike or hymn to his mum. But the physicist, as he fleetingly acknowledged, was an ageing bourgeois in the grip of stereotypical thinking. Tarpin was too old for a body piercing, but sitting right on the skyline of his shoulder, protruding a good half-inch, was a growth of twisted skin, a tag, that resembled a miniature human ear, or a sailor’s minuscule parrot. A few turns of tightly tied dental floss and it would be gone in a week, but perhaps women were touched by such a flaw, by such vulnerability in so large a man with his own business and three employees. Patrice’s tongue would surely have explored its tiny folds.