Without guilt we would all be monsters.

My mother had a china plaque on the kitchen wall that read: Do remember to forget, anger, sorrow, and regret. I've always felt this to be bad advice, if not for the individual then for the society they live in. We need to remember our failures, our wounds, our losses.

"Leave some milk!" I reached to stop Mary raising the end of the carton any higher. "And those things are ninety percent sugar already. Don't go adding more."

Mary scowled at me from beneath a blonde fringe, pure venom, replaced by a sunny smile in the next moment. Her ability to freefall through the emotional spectrum might have been down to being ten, or due to being close to ninety percent sugar herself, or simply a permanent feature gifted to her by an absent mother.

"Sarah will pick you up from school," I said.

"Good. She does it better than you." Mary set the milk carton down. It sounded suspiciously empty.

"Don't play her up." Sarah was one of two women I paid to look after my daughter after school until I got back from work. Of the two she was the more nervy one, prone to calling me at the lab over a knee skinned in the playground or the appearance of a mystery rash.

"Helen Anderson still talks about when you tried to kidnap her." Mary had more to say but opted to render it unintelligible by spooning a large amount of crunchy milk-drowned sugar cereal into her mouth.

"I just thought she would make a better daughter is all," I said. "She seemed very polite."

Some people never forget a face. Others are bad with faces. What is seldom understood is that this talent for recognition is a spectrum that goes to extremes on either side. It's well known, among brain surgeons at least, that there is a localised area of the temporal lobe that has evolved to recognise faces. In me, that part of the brain didn't develop properly. It leads to a condition called prosopagnosia, which essentially means that, while I can remember how to spell prosopagnosia and as many phone numbers as I need to, if my mother rang the front doorbell right now I would open it and enquire politely whether I could help her.

To compensate my failings in the recognition department I use other clues such as context, clothing, facial hair, and accessories. Unfortunately Helen Anderson happened to be the same height as Mary, have the same long blonde hair, and on that day the same vacuous boy band on the same satchel. She was even wearing identical red hair slides set with little plastic Hello Kitties.

The police weren't called, but it had been a near thing.

"Sarah will be staying late tonight and putting you to bed at nine. I don't want to hear that there was any fussing. I'll be back around eleven."

"Why, what are you doing?" A question worth pausing the sugar delivery system for.

"I'm going out after work."

"With Dave and Mo?" Mary asked. "Will Rachel go too? Where are you going? Why can't I come? I-"

"Not with them, no." I would have lied but I've never been good at it.

"You're going on a date!" Her eyes widened then narrowed.

"It's a friend of Rachel's, and no you can't come, it's after your bedtime."

It took another fifteen minutes to lever Mary out the front door into a light drizzle.

"Everyone else drives their kids to school."

"Walking is good for you. Builds character."

"Mrs Robbins says I have too much character already." She closed the gate behind her.

The mile between our house and the school was residential streets, a park that was essentially a two acre field of neatly mown grass, and a suburban high street. At a younger age I'd walked twice the distance through London every day to reach my school, and without the benefit of a mobile phone or lectures on stranger danger. The looks I got at the school on parents' evenings would make you think that by letting her walk there I was advertising my daughter on paedophile websites rather than merely accepting that her whole life would be fraught with scores of minute risks none of which were ever likely to happen.

My day passed without incident as they generally do. I left the laboratory late and on foot, aimed for my blind date. That's part of the beauty of Oxford, everything is within walking distance. At least if, unlike most of my generation, the idea of walking a mile doesn't make you throw up both arms in a mixture of horror and surrender. Mo, the fittest man I know, drives a sleek black thunderbird which he surely can't afford, to get him the thousand yards to work. And later he drives it the two miles to Golds Gym, wherein he pounds out half-marathons on their running machines in ridiculously short times. I would tell you the make of the thunderbird if I could, and Mo would be devastated to learn that I can't, but I'm not good with cars. Better than I am with faces, but not good. It's black though. I'm sure of that. Blackish.

The restaurant was Italian, Al Bacio. Whether that meant something in Italian or was the name of the owner I couldn't tell you. I said to Rachel that I should meet her friend in a pub. Why would anyone have a blind date in a restaurant? Watching someone eat is surely second only to watching the other end of the process in terms of attractiveness. Rachel had said "Ewwww!" in much the same way that Mary often did, though Mary had the excuse of being ten. Rachel went on to say that in a pub nobody can hear themselves speak let alone what anyone else has to say. The people that own pubs turn the music up so loud that the only thing left to do is drink. I countered with the suggestion that my date and I were more likely to form good opinions of each other if we didn't hear anything the other one said.

"It's not as if the last two were sterling successes," I'd said.

"Well, no," Rachel admitted between devouring bites of her homemade sandwich and tapping absently at a screen of tabulated data.

"And I bet I'm not the first person you've tried to set this Kara up with."

"Well..." More tapping, another bite stealing a full third of the sandwich. "No." Muffled around her mouthful but unmistakable.

"How many?" My mind leapt for a number. "Ten?" Rachel knew a lot of people, most of them from the lab and most of them male.

"She's quite picky."

"Great."

There are people who have a certain animal magnetism. They're easy in their skins and something in their body language draws you right in. The allusion to magnetism is apt since magnets have two poles and when set the wrong way can repel each other with just as much force as they attract. There are two types of animal magnetism and I seem to have the wrong sort. So 'picky' isn't likely to work. Desperate is more my demographic.

Al Bacio's stood at the end of the Greenwich Road high street, a seemingly random selection of smaller shops and restaurants built into a converted Victorian terrace. It had a depressingly modern and bright décor, at odds with the Oxford chic where anything post-Dickensian is held to be an eyesore. The sign, white, red, and green, and glowing from within, was hard to miss.

I went inside, hunched beneath a sort of generalised guilt that I couldn't put a name to. As if I were up to something nefarious, here on false pretences. Which, to be honest, is how I feel anytime I'm called on to play a proper functioning adult.

I'd arrived early of course and asked for a table for two by the window, though a dark corner would have suited me fine had Al Bacio's sported any shade. I had to arrive early because the chances of this Kara spotting me were much greater than the reverse.

Rachel had got me these three dates on the strength of my photo and an artful collection of half-lies. She maintained that I was in no way hard on the eye, a claim for which I had to take her word. To me faces are faces. I can no more ascribe attractiveness to one than to the arrangement of soup cans on the supermarket shelves. Bodies, on the other hand, I can appreciate. That one I tend not to mention on a first date. If the face thing comes up, and I strive manfully not to let it, then I spin it as meaning that it's the inner person that attracts me rather than superficialities like the subtle balance of nose and chin, and the size and spacing of the eyes. To hear women talk you would think this would be a big plus in the 'nice guy' column, but it turns out that the women I meet generally want me to be attracted to them because of their looks rather than their winning personality.

So I sat and watched the traffic, still feeling guilty. I'd actually woken up feeling guilty, but that had been specific if still undeserved. I'd had a worryingly convincing dream where for reasons now forgotten I had needed to bury the body of a person whose death I had caused. I'd woken an hour before my alarm, burdened with a crippling anxiety that I might be caught and an equal weight of guilt concerning my poorly defined crime. Running water ... something to do with water and stones, that's all I managed to hold onto and even that was slipping away. Whilst it was a relief to realise that it was all nonsense both sensations continued to nag me through the day.

Guilt is a strange thing. Like my underdeveloped face recognition some of us humans have an overdeveloped capacity for guilt. They're keen to confess, ready to concede their role in anything shady no matter how peripheral it might have been. For some all it takes is seeing a murder reported on the TV and before long they're marching themselves to the local police station to claim responsibility.

As my grandmother would say, far too often for it to sound wise, "There's nowt so queer as folk."

"Hello? Alan is it?"

I looked up. The woman was already sitting down. She had long chestnut hair with a slight curl to it, her blue dress was buttoned at her collarbones and she wore a necklace of slightly iridescent metal shapes, triangles, rectangles, and ovals.

"Hi, you must be Kara." I met her gaze and smiled. She seemed slightly familiar but then most people did. My life was a masked ball where the masks never came off.

Kara settled and took the menu from the waiter who followed her over. We ordered and made small talk about how we knew Rachel. Kara was new in town and had met Rachel at the gym. It seemed like everyone I knew spent half their life sweating away over personally crafted exercise programs. Sport and I had been strangers since I entered the sixth form at Goldsmiths and left mandatory P.E behind. I had a reluctant agreement with myself that I would do something energetic if I showed any signs of becoming fat, but since my father had stayed rake thin until his mid-forties the chances were that I wouldn't have to call my own bluff for well over a decade yet.

"So, you work with Rachel? It sounds exciting!" Kara smiled and sipped her wine, offering me the stage.

"It does sound exciting." Most people's impression of forensic science is formed from police procedural shows where we stand in our white overalls amid crimson crime scenes. My eternal quandary, like the A&E nurse, was whether to pop the bubble and report the reality as opposed to the fantasy. The smart money would play up to the illusion and reap the rewards of seeming more interesting by association. But I'm bad at lying. "It's a lot less exciting than you might think though."

"Oh?" She sounded disappointed. "Rachel tells me she was at a murder scene just last week..."

"We don't get many of those around Oxford." I sipped my Chianti, aware that I was banging the nails into the coffin of any future in which Kara took me to her bed. "Rachel was at the scene of a disturbance. It might be murder. But we need to find the missing person first before we know if they're dead or alive. Anyway," I soldiered on along my truth march to loneliness, "only some of us actually go to crime scenes. Rachel specialises in collecting evidence, and back at the lab she does fibre analysis. I stick to the lab. I'm part of the DNA team. I split my time between routine analysis and researching new techniques." Much more of the former than the latter if I'm honest, but I decided that Kara had had her fair share of my honesty.

The meal arrived. She'd asked for garlic bread so I had too. However long the odds it pays to be on the same page regarding garlic if there's even the slightest chance of a goodnight kiss. I selected a pizza for safety, funghi in case she was vegetarian. Spaghetti and I have a love hate relationship. I love it but it hates me and slaps me around the chops whenever I eat it, reducing me to a passable imitation of a vampire who's drained one virgin too many and made a messy job of the last one.

"So why forensics? Why DNA?"

At least she sounded as if she knew what DNA was. "Well." My chance to play the sympathy card. The sympathy card had 'Michael' written on it, my twin, abducted at eight, body never found. Those were the facts and the elaboration was a heart rending story of justice sought through the power of science, idealised in a young mind as a core of calm and certainty in a world that lacked sense or structure. But I'd grown tired of sympathy long ago, and while the facts were true the rest of it was mainly not. I probably would have followed the same path anyway. I certainly would have ended up in a lab coat. "Codes have always fascinated me," I said. "If you think about it the most wonderful book you've ever read, the most heart rending love letter, the most momentous news, have all just been combinations of twenty-six letters with some punctuation scattered in. All that complexity held in reorderings of the alphabet. And the humans behind those stories, who lived those things or dreamed them up out of imagination ... they're all built from something smaller than a grain of sand using another story, a set of instructions written using just four letters."

Kara popped a meatball into her mouth and chewed before saying. "And all the programs ever run on a computer are explained to it in just two letters ... which happen to be digits. One and zero."

"Ah... You computer people have to win everything."

She laughed at that, which was kind because it wasn't funny, and afterwards we managed to chat easily about all manner of nothing. I told her about Mary who had been practicing at being a teenager for the past four years and would be a horror when she finally got to be a real one. Kara told me about her younger sister who had run away at fourteen to live with a thirty year old. I told her about my wife who had run away at twenty-seven to pursue a fulltime relationship with vodka. All the usual first date chat.

Before I knew it my watch was beeping, letting me know I had fifteen minutes to get back before Sarah was due to leave. I raised my hand for the bill. "Duty calls."

Kara put down her coffee. "Awww."

"Sorry. My babysitter is-"

"No, I mean it's sweet to see a man with a sense of responsibility."

"I'll take sweet." I caught the waiter's eye and then looked back at Kara. "I mean if 'ruggedly handsome' or 'irresistibly charming' aren't on offer."

"That's sweet too," she said.

"Look, I do have to go. I didn't realise how late it had got. Can I just leave this with you?" I put down a twenty pound note to cover my half of the bill and a fair chunk of hers. I stood. "It was very nice to meet you, Kara."

"So formal." Another smile, this one showing an array of even white teeth. "Maybe you should take my number."

"Hit me." I'd set the alarm thinking I could get a taxi home but I'd forgotten to order one and the high street looked empty. I would have to hurry and even then I'd be five or ten minutes late.

Kara started to root in her handbag for a pen.

"I can remember it," I said, eyeing my coat.

"That's right!" She brightened. "Rachel said you were one of those ... memory masters!" She fired off a string of numbers. "All locked away."

"I think so." I repeated them.

"Perfect."

"I do have to go. Sorry." I hovered for a moment. Should I bend awkwardly for that kiss and face a well-lit rejection on display to anyone who might be passing? I wimped out and offered her my hand instead. She took it in hers as if we were holding hands in the street rather than shaking, and smiled up at me, amused.

"I'm pleased to tell you, Mr King, that you have passed the interview stage and I look forward to our next meeting."

I made an awkward laugh and began my escape.

"Just ask Rachel for the number if you forget," she said as I reached the door.

"Memory guy." I jabbed a finger at my forehead. "I won't forget." And with that I was out into the cold night, laced with the same drizzle that had been falling since dawn. I muttered a complaint. September is still summer in my opinion and it should damn well behave like it. Leave autumn for October to play with.

I strode home at a pace just shy of uncomfortable and wrapped in the chill of increasingly fine drizzle. My memory for facts and figures is fairly average. For life in general it's really quite bad. I got by in school and then university by being clever. The science subjects don't require reams of facts to be stored, they require you to understand difficult things. I'm OK with that.

Rachel told Kara I was a memory master. There's actually an internationally recognised test you can take in order to claim that title and, with perhaps less shame than I should, I will admit to taking and passing it. I don't have a photographic recollection of scenes. I was never a high flier in French class, able to reel off irregular verbs. But as a student, interested in the subject because of my peculiar failing with faces, I did train myself in the tricks that allow even us regular mortals to perform feats of memory that seem extraordinary.

They say it started with scribes back in the days when civilisation was just beginning to get complicated. The days when our lives started to stack up more potentially useful facts than a man could easily lay his hands on at once. The practice of building memory palaces, of organizing memories into visual processes encoded into the architecture of an imaginary palace was a start. The 'cheap trick' that lets me memorise the order of a shuffled card pack in a couple of minutes is to encode the suits and numbers into visually startling images and to link those images in a story. I remember the story and the images, and that seals the random order of fifty-two different things into my mind. A variant of the technique works for number strings. I can tell you Pi to ten thousand places. Nobody ever wants me to. As a party trick it has strictly limited appeal. But I'm good at it and when we discover something we're good at we tend to stick with it.

When I was small I wondered if a person could remember the whole of their own DNA sequence and have the entirety of a human being recorded in their mind. But that would require memorising three billion base pairs, and while I'm good at it ... I'm not that good. Also, if you give it a moment's thought it's entirely pointless cramming that vast amount of information into the less than two kilograms of brain you possess when the same code is there in each of the invisibly small cells that make you up. It remains in its entirety in every fingerprint you leave behind.

"Had a good time?"

I was digging for my keys at the door, still on autopilot, and Sarah opening it made me jump, though I managed to avoid a cry of alarm.

"Yes, thanks." I realised as I said it that I had had a pretty good time. Far more relaxed than on the previous two dates Rachel had set up for me. Whether that meant that Kara had too I couldn't say for sure. But she had given me her number. "Mary been good?"

Sarah waggled her hand. I'm not a great judge but I thought she looked tired. "She went up to bed without a fight but she said she wasn't going to sleep until you got home."

I waved Sarah off and walked soft-footed into the living room. The sofa received me in its musty embrace and I thumbed through the messages on my phone. The outline of Kara's hips beneath that blue dress swum up from somewhere to interrupt me and I spent a pleasant few moments dwelling on it. I had liked her. She felt comfortable and exciting at the same time. I would call her. The number chain danced behind my eyes.

Among the Facebook alerts and belated birthday wishes from Great Aunt Jane, who I felt at ninety-eight was too old to own a smartphone let alone be texting, there were five messages from Rachel. The first two were the predictable inquiries about Kara. Rachel seemed to feel she owned a stake in any relationship that resulted from her matchmaking.

> She's HOT, yes? I told you so.

> Where are you both? Are you two shagging already?

But the next three were unexpected.

> They found her!

> My missing person. Messy one :(

> Wood Farm. By the bridge. Get in early, lover-boy. Lots of samples. Rush jobs.

I pinched the bridge of my nose, suddenly tired. Wood Farm was an estate on the edge of town bordering a hundred acres of woodland. There were a few streams. The only bridge there would be as old as the University if it were original, a clapper bridge built of slabs of raw stone. A Victorian folly though, rather than a work of medieval peasants.

I knew that particular bridge well. In my mind I'd travelled there again and again. The sense of guilt that had dogged me all day surged and bit hard.

"Daddy?" A small voice at the doorway.

"Mary! What're you doing out of bed."

"A dream." She rubbed her eyes, still half asleep. "A bad dream, Daddy."

It seemed to be the day for them.