Jackson could feel the ache in his jaw starting up again. He was currently seeing more of his dentist than he had of his wife in the last year of their marriage. His dentist was called Sharon and was what his father used to refer to as "stacked." She was thirty-six and drove a BMW Z3, which was a bit of a hairdresser's car in Jackson 's opinion, but nonetheless he found her very attractive. Unfortunately, there was no possibility of having a relationship with someone who had to put on a mask, protective glasses, and gloves to touch you. (Or one who peered into your mouth and murmured, "'Smoking, Jackson?")

He opened an out-of-date copy of Le Nouvel Observateur and tried to read it because his French teacher said they should immerse themselves in French culture, even if they didn't understand it. Jackson could only pick out the odd word that meant anything and he could see subjunctives scattergunned all over the place – if ever there was an unnecessary tense it was the French subjunctive. His eyes drifted drowsily over the page. A lot of his life these days consisted of simply waiting, something he would have been useless at twenty years ago but which he now found almost agreeable. Doing nothing was much more productive than people thought; Jackson often had his most profound insights when he appeared to be entirely idle. He didn't get bored, he just went into a nothing kind of place. He thought sometimes that he would like to enter a monastery, that he would be good at being an ascetic, an anchorite, a Zen monk.

Jackson had arrested a jeweler once, an old guy who'd been fencing stolen property, and when Jackson came looking for him in his workshop he'd found him sitting in an ancient armchair, smoking his pipe and contemplating a piece of rock on his workbench. Without saying anything, he took the rock and placed it in Jackson 's palm, as if it were a gift – Jackson was reminded of his biology teacher from school who would hand you something – a bird's egg, a leaf- and make you explain it to him rather than the other way round. The rock was a dark ironstone that looked like petrified tree-bark, and sandwiched in the center of it was a seam of milky opal, like a hazy summer sky at dawn. A notoriously tricky stone to work, the old man informed Jackson. He had been looking at it for two weeks now, he said, another two weeks and he might be ready to start cutting it, and Jackson said that in another two weeks he would be in a remand prison somewhere, but the guy had a great lawyer and made bail and got away with a suspended sentence.

A year later Jackson received a parcel addressed to him at the police station. Inside there was no note, just a box, and in a nest lined with midnight-blue velvet was an opal pendant, a little plaque of sky. Jackson knew he was being given a lesson by the old man, but it had taken him many years to understand it. He was keeping the pendant for Marlee's eighteenth birthday.

Nicola's husband, Steve Spencer, was convinced his wife "had taken a lover" – that's how he put it, so it sounded delicate and rather courtly to Jackson 's ears, whereas most of the suspicious spouses who came to him tended to voice their mistrust in cruder terms. Steve was the nervy, paranoid type and he couldn't understand how he'd managed to net someone like Nicola, because she was "so gorgeous." Jackson had known "gorgeous" in his time and it wasn't the Nicola Spencers of the world, although he thought that if he was married to Steve Spencer he might be tempted to "take a lover." Steve was a pharmacist in a chain of drugstores and seemed to have no hobbies or interests other than Nicola. She was "the only woman in the world" for him. Jackson had never believed that there was one person in the world that you were destined for. And if there was, knowing his luck, she'd be working in a rice field in the middle of China or be a convicted killer on the run.

When she wasn't at work, Nicola Spencer went to the gym, to Sainsbury's (and once, for no apparent reason, to Tesco's), to her mother's, to the homes of a friend called Louise and a friend called Vanessa. Vanessa was part of a married couple – Vanessa and Mike – who were also friends of "Steve and Nicola." Louise and Vanessa, as far as Jackson could tell, didn't know each other. Nicola also went regularly to the garage, for petrol obviously, and in the garage shop she sometimes bought milk and nearly always bought chocolate and a copy of Hello or Heat. She had also been to a garden center, where she bought a tray of bedding plants that she had put straight into the garden and had then failed to water, judging by the look of them when Jackson climbed up on the garden fence to have a snoop at what went on chez Spencer, or, more accurately, au jardin Spencer.

In the last four weeks Nicola had also been to a DIY superstore, where she bought a screwdriver and a Stanley knife, to Habitat, where she bought a table lamp, to Top Shop for a white T-shirt, to Next for a white blouse, to Boots (twice for cosmetics and toiletries and once with a prescription for Ponstan), to Robert Sayle's for two blue hand towels, and to a fish stall on the market, where she bought (expensive) monkfish for a meal – for the aforesaid Vanessa and Mike – which Steve Spencer later reported to have been "a disaster." Nicola was apparently not a great cook. She also led a bloody boring life, unless something fantastically interesting happened to her when she was pushing a trolley up and down the economy aisles of her airline. Is that what had happened to Josie when she "took" David Lastingham? Was she just so bored with Jackson that she couldn't bear it anymore? She met him at a party, a party that Jackson hadn't gone to because he was working, and the pair of them had "tried to control their feelings" but they obviously hadn't tried hard enough because within six months they were taking each other at every available clandestine opportunity and now David Lastingham got to put his penis in Mummy's vagina whenever he felt like it.

Josie had filed for divorce as soon as it was possible. Irretrievable breakdown – as if it were all his fault and she wasn't shagging some poncy guy with a goatee. ("David," Marlee said, not as grudgingly as Jackson would have liked. "He's alright, he buys me chocolate, he makes nice pasta." It was a six-lane motorway from that girl's stomach to her heart. "I cook nice pasta," Jackson said and heard how childish that sounded and didn't care. Jackson had got someone he knew to look up David Lastingham on the pedophile register. Just in case.)

Jackson smoked the last cigarette. Nicola hadn't done anything the least suspicious on Jackson 's watch, so if she was having an affair then she must be literally playing away from home – all those stopovers in midrange hotels, warm evenings, and cheap alcohol provided the perfect conditions for fostering bad behavior. Jackson had tried to explain to Steve that he was going to have to pay for Jackson to fly with Nicola if he really wanted to find out if anything was going on, but Steve wasn't keen to fund what he seemed to think would be a free holiday abroad for Jackson. Jackson thought he might just go anyway and then do some creative accounting when it came to the bill, a return trip to almost anywhere in Europe could easily disappear into the catchall heading of "Sundries." Maybe he would wait until she was on a flight to France and tag along. Jackson didn't want a holiday, he wanted a new life. And he wanted to be finished with Nicola Spencer and her own dull life.

When Jackson set up as a private investigator two years ago he had no expectation of it being a glamorous profession. He'd already been a member of the Cambridgeshire Constabulary for twelve years and before that he was in the military police, so he had no illusions about the ways of the world. Investigating other people's tragedies and cock-ups and misfortunes was all he knew. He was used to being a voyeur, the outsider looking in, and nothing, but nothing, that anyone did surprised him anymore. Yet despite everything he'd seen and done, inside Jackson there remained a belief- a small, battered and bruised belief- that his job was to help people be good rather than punishing them for being bad.