Turns out time travel does not get you the morning off work.

I found this out at 8:52 the next day, stood dead still in the trainer aisle of Sportskit, the big soulless sports megastore on the retail park off the A13, staring at a wall of football boots like I’d seen the actual face of God, when a voice I hadn’t heard in sixteen years sliced right through me.

"MERCER! You are not paid to admire the stock!"

Dean.

Oh, Dean. My supervisor.

A weaselly little man who’d done a two-day "Leadership in Retail" course in 2008 and had not shut up about it for a single shift since, who wore his lanyard like a war medal and called customers "guests" and once wrote me up for "negative body language near the replica kits."

I had forgotten Dean existed. I had spent sixteen years successfully forgetting Dean existed. And here he was, alive, twenty-eight, gelled, vibrating with the tiny power of a man in charge of nothing.

And here’s the thing I understood now that I hadn’t understood the first time round, back when I’d just hated him.

Dean wasn’t a villain.

Dean was frightened.

Twenty-eight years old, and this lanyard, this little laminated scrap of authority over a trainer aisle, was the most anyone in his whole life had ever trusted him to be in charge of, and he clung to it with both hands because somewhere underneath the gel and the leadership patter he knew, he knew, that this was it.

This was as high as the ladder went for Dean. In my other life he was still here when I was forty. Assistant manager by then. Still gelled. Still vibrating. Still telling work-experience kids about a two-day course he’d done before they were born.

There’s a particular kind of sad in a man like that, and once you’ve clocked it you can’t quite manage to hate him any more. You just want to get him a cup of tea and tell him it’s not his fault.

Didn’t stop him being a colossal pain in the backside, mind.

"Sorry, Dean," I said. Sorry, Dean. God, my whole life used to be those two words.

And here’s the bit that got me, standing there in a polyester polo two sizes too big with SPORTSKIT: ASK ME ABOUT OUR LOYALTY CARD stitched over the heart. Six months. That’s all it had been, in this life.

Six months since a lad twice my size went through the back of my knee in a reserve game for a club that didn’t even bother phoning to tell me I was released, they just stopped putting my name on the team sheet until I got the message.

Twenty-three years of dreaming, gone in one crunch. And I’d ended up here, folding tracksuits and selling shin pads to nine-year-olds who’d go on to have better careers than me, because what else is a failed footballer good for.

In the other life I’d stuck this job out another fourteen months before I scraped enough together to do my coaching badges. Fourteen more months of Dean.

Not this time, sunshine.

"Tell you what, Dean," I said, and I felt the smile spread across my own young face like sunrise. "Hold that thought. Hold it for about three weeks."

"What?"

"Nothing. Where do you want these Predators."

Because I couldn’t quit. Not yet.

That was the agony of it. I had a head full of the entire future and forty quid in a bookies and not one single penny to my actual name, and I had to clock in, and scan trainers, and say "lovely, that, great choice" to a man buying his kid the wrong size, for sixteen more days.

Knowing. Knowing.

It was like sitting on a winning lottery ticket made of solid gold while the bus driver tells you the machine’s broken, come back a fortnight Tuesday.

And the job itself, God!

Let me paint you the picture, because there is nothing on this earth quite as character-building as minimum-wage retail when you spent your whole childhood thinking you’d run out at Wembley.

Five pounds ninety-three an hour, that was the going rate in the summer of 2010, I know because I once worked out my hourly wage out of pure spite while folding a wall of Brazil shirts.

Thirty-odd hours a week if Dean was fond of me that month, twelve if he wasn’t, never quite enough to build a life on, which is sort of the whole idea of a job like that.

I’d haul the security grille up of a morning, RRRRRATTLE, hoover a shop floor the size of an aircraft hangar, and then spend eight hours performing the holy trinity of British retail: folding things that did not need folding, telling people we hadn’t got it in the back when we very much had got it in the back, and strong-arming knackered parents into a loyalty card that earned them roughly forty pence a decade.

Lunch was a meal deal eaten standing up in a stockroom that smelled of cardboard and fresh rubber.

And every hour or so, regular as the tide, some little kid would come in gripping a fiver of birthday money for a pair of shin pads, eyes shining because he was going to be a footballer, definitely, and I’d ring it through and say "good luck, son," and not let a single thing show on my face.

That was my whole little life. Six months out from the only dream I’d ever had, and reduced to that. So you’ll understand why I held onto those sixteen days the way a drowning man holds onto a lilo.

So I waited. And while I waited, I started.

That first night, after my shift, instead of slumping in front of the telly with a four-pack and a kebab like every other knackered evening of my old young life, I dug out a pair of battered trainers, and I went for a run.

Bloody hell, it was awful.

I got about four hundred yards up Carling Street, slap, slap, slap, wheeze, before I had to stop and hold onto a lamppost and have a serious conversation with my own lungs. And, while we were at it, my left knee.

The left knee that a lad twice my size had gone through the back of in a reserve game six months ago, that had managed about three minutes of asphalt before going twinge, then twinge, then no, mate, absolutely not, sit me back down on the sofa where I belong.

At twenty-four years old, I was blowing like a fat dog in a heatwave because twenty-four-year-old me lived on energy drinks, Rizlas, and despair.

A couple of kids on bikes rode past, and one of them shouted, "RUN, FATTY!" which was rude because I was not even that fat, but also completely fair.

Fuck them kids.

But I did it as I continued running. Half a mile, that first night. Pant, pant, pant.