‘Vauxhall, Lambeth, Waterloo. Umm … Southwark? No, Blackfriars. Then Southwark, right?’

Ash nodded, not taking her eyes off the A–Z she was holding up in front of her like a hand of cards.

‘Go on.’

But I was lost. Further down the river was Tower Bridge, I knew that. But whatever lay between that and Blackfriars was a mystery. Were there any other bridges? What about Chelsea Bridge? Where did that come in? Wasn’t there a railway bridge somewhere? And was there anything beyond Tower Bridge?

‘Can I have a quick look?’

Ash handed me back the A–Z and I swept my eyes along the river again, west to east, noticing that Blackfriars did indeed come before Southwark, and that between them lay the Millennium footbridge, which I’d forgotten. And just to the north lay the tangle of the City, radiating out from the Bank junction, where eight roads meet, and where I had never successfully ridden through without taking a wrong turn and ending up in a very different place from what I had planned.

‘I’m never going to learn all this!’ I exclaimed despairingly.

‘You don’t need to learn all of it now,’ Ash reassured me. ‘Alex said they’ll test you on things like the bridges, and the routes through Soho, and you can just pick up the rest of it on the job.’

I let myself be comforted by this, even though Ash probably had no better idea than I did about how these things worked. She had only been my girlfriend a few weeks, and we had found each other at similar stages of life: her at the end of a web-developer contract; me at the end of a master’s degree; both of us without a plan or a purpose, thinking that couriering might be an enjoyable alternative to the responsibilities we had recently abdicated.

Had I not met someone with the same ambition, my own might well have continued to lie dormant – like many other paths in life I’ve pondered at length, idly or actively, but not taken. Becoming a cycle courier seemed just as likely as becoming a surgeon or a firefighter – by no means impossible, but so far removed from my narrow rounds of temp jobs and postgrad applications that it might as well have been. Until a couple of years before I started couriering, I didn’t even know there was such an occupation, and planned to make my living using my mind rather than my legs. And when I first strapped the radio to my bag in 2008, I envisaged the job as a short adventure rather than a career – something I’d do for six months or so, and which would give me a good story to tell in years to come, when I’d rejoined the real world, and found a sensible, responsible way of earning my money.

My first encounter with a courier was shortly after I left university, and didn’t feel particularly fateful. I had moved to London for no particularly good reason and was working as a part-time receptionist in Camden, struggling to stay afloat, and to make sense of the expanse of the city after the small market town I’d lived in for the past four years. Once, I’d innocently decided to stroll into the city centre for the evening (I was living in Ealing at the time, and had noticed that if I followed the Uxbridge Road east for long enough it would turn into Oxford Street), and been shocked when it took me over three hours.

If I tried walking in the opposite direction, I never managed to find the point at which the city met the fields, a line that in smaller towns is much more clearly demarcated – the final row of houses will overlook the countryside, and that’s that. It wasn’t that I was entirely unused to large cities – I’d spent summers in Vancouver and Barcelona, and found their noise and bustle and profusion exhilarating, rather than intimidating, after my quiet childhood in rural Wales – but London was of a different order of magnitude. My flat, my various jobs, and the few friends I had all seemed to be at least an hour’s tube ride apart from each other, far too scattered for any sense of neighbourhood, and I travelled to job interviews in mysterious, far-flung places like Colindale and Dulwich, confidently following the different-coloured tube lines, but often with only the faintest idea of where I would actually end up, and of how these places fitted into the maddening sprawl that was London.

One afternoon, I was sitting at my reception desk, as usual, watching the world go by with alternating fascination and boredom. Although I was getting used to the repetitiveness of my working day, the thrill of being part of it all hadn’t quite worn off. I still felt a little as if I was play-acting when I rubbed shoulders with the other commuters on the tube, and joined the chorus line queuing to buy morning coffee. I drank in all the different people who passed through reception, noticing what they wore, how they acted, how they expected to be treated; not yet knowing how I wanted to live my own life, and wondering if I’d want to live theirs.

I watched the women in suits being escorted upstairs for a meeting; the van drivers who wheeled in boxes of stationery and cleaning products on trolleys; the cheerful young men who delivered sandwiches from bicycle trailers. And then a girl of about my own age appeared on a sleek black bicycle. She was blond and petite, and wearing frayed cut-off jeans over her cycling shorts. She leaned her bike against the plate-glass window without even locking it, strode through the revolving doors, briskly handed me an envelope, held out her clipboard for me to sign, and within seconds was back on the bike, standing tall on the pedals for a couple of strokes, and then swooping off towards Oval Road.

I remember very clearly how I felt as I watched her disappear round the corner. If only I was the sort of person who could do that! I imagined us as opposites – I was sitting placidly behind reception; she was outside riding her bike around the city. It was a novelty to me that you could ride a bike in a city. I wondered how different I would need to be, to be able to live my life the way she must live hers; what different turns I would have had to take in my teens and my childhood to have the courage to cycle through heavy traffic, the ingenuity to find my way through the city and fix the bike when it went wrong, the resilience to live what looked as if it must be an exhilarating but also a chaotic and precarious life. It wouldn’t occur to me for another three years that I could, in fact, cast off the pinstripes and go and join her.

I was, of course, by no means the first person to be swept away by the romance of the cycle courier. As I began commuting by bike and making friends with other cyclists, I discovered that couriers were, for many, the heroes of the scene; that I wasn’t the only one who rode the seven miles to work and wished that I could just carry on all day. I noticed them more and more, shooting through the traffic ahead of me, radios crackling. Sometimes I’d try to keep up with one, following his lines between the cars, copying his hesitations and accelerations and the way he balanced his bike through the curves, mustering the confidence to ride through smaller and smaller gaps when I saw that he made it through them just fine. Usually, he (they were always men) would lose me when we got to a red light, where I’d stop and he’d race straight across the junction, a split second before the traffic surged in. Whenever a courier delivered to an office where I was working, I’d gaze at him like an awestruck schoolgirl, desperate to identify myself as a fellow cyclist, and to ask him about his job, but too shy to puncture his surly mystique. Couriers are splendidly anachronistic figures – in an age where almost everything is mechanised and digitised, where the vast majority of our communications are sent electronically, and where navigating a capital city involves sitting in taxis in traffic jams, or paying money to use London’s highly sophisticated public transport infrastructure, seeing actual human beings on bicycles darting among the traffic to deliver packages seemed almost equivalent to spotting Roman chariots racing between the buses on the Euston Road.

Part of the courier’s romance, I realised, came from this incongruity. He was, manifestly, a human body among machines – but he was also, apparently, the equal of these machines, and therefore quite possibly superhuman, as well as a heartening reminder that, despite the advances of technology, there will always be a place for, and a need for, flesh and bone and muscle. Couriers seemed to me at once to have sidestepped society, and yet to be ubiquitously visible within it, striding sweatily into my reception with a package, pedalling alongside the bus for a moment before disappearing into the traffic jam ahead, sitting at the tables outside my habitual sandwich shop, radios blaring – a constant reminder to disillusioned wage slaves like me that there is another side to the desk, and a whole world outside the office.

I still hadn’t quite memorised the bridges when I turned up at the Pink Express offices near Vauxhall Bridge, masking my nervousness with a layer of calm bravado.

But there was no test, and no interview. I’d been told to ask for Derrick, who was the fleet manager, though no one had bothered to tell me that. He was a jovial, steel-haired man, a few years off retirement, with tattoos on his forearms, and a paternal air that I was later told could turn very nasty, given the wrong provocation. His office was tiny and windowless, screened off from the main warehouse by plastic partitions, and, apart from his desk, contained nothing but a large filing cabinet, a set of coat hooks, hung with...