Joel glances at me and smiles. It’s OK. He’s forgiven me for lying to him about the CPR.

Forgiven me for saving his life.

I need to change the subject. ‘So . . . what’s happening here?’

‘It’s our rehab class,’ Steve says, laying out more pieces of equipment. ‘Joel’s been coming for a few months now, haven’t you, kid?’

Is this drug rehab? But the people who’re arriving behind us don’t look like thrill-seekers. Mostly they’re portly men of my dad’s age or older, except for one skeletal younger guy who seems barely able to take more than a few steps at a time. There’s a Christmas theme: Santa hats, velour reindeer antlers, snowflake socks.

Joel is next to me. ‘Guessed yet?’

When I shake my head, he unzips his fleece – his T-shirt rides up, revealing his flat belly and the line of hair disappearing down past his waistline. I have to look away.

‘Ta-da!’ he says, pointing at the logo on his top.

‘Coast Along Heart Charity,’ I read aloud. ‘Oh! This is cardiac rehab.’ I smile, but it’s not good news. Joel’s confidence – or his health – must have taken a nosedive to be going for something this gentle after completing our triathlon: cardiac rehab is for heart patients who can barely climb the stairs.

‘Starter’s orders, guys and gals!’ Steve calls out, and people take up stations in different parts of the gym. ‘Any hospital admissions in the last week, symptoms you need to report? No? Excellent job. Music, maestro, please!’

It’s Joel who turns on the CD player and the urgent rhythm of ‘Another One Bites the Dust’ blasts out of the speaker.

Joel walks over to Steve at the front, winks at me and claps his hands in time to the music. ‘All right, let’s warm up with a light march.’

He’s not participating in the class: he’s leading it. What a relief.

He catches my eye and grins. ‘And that includes you, Kerry Smith! There are no shirkers here.’

Joel encourages, cajoles, laughs, performs. He’s good. Very good.

And as he demonstrates the exercises, he has his grace back. I haven’t seen him move so effortlessly since the last night of 1999.

Joel and Steve take it in turns to lead different sections, making a great double act. CPR anthems keep popping up – ‘Stayin’ Alive’, ‘I Will Survive’ – and I realize it’s an in-joke, and that the gallows humour that keeps us sane in the ambulance control pit is important to these patients, too.

After the class ends, Joel comes over, his face and body glowing. ‘Well?’

‘I approve! What gave you the idea?’

‘After the triathlon, I realized I’d been moping about for roughly four years too long. Decided I needed something else to do. I googled “heart” and “volunteering”.’