‘You’re so lucky to be training,’ he said, as he drove me through one of his favourite circuits. Ten three-minute rounds banging the pads with ten burpies and twenty press-ups instead of a minute’s rest in between, Fred slapping me round the ear with a cracked leather pad whenever I dropped my guard, the rounds passing until I lost count, until I was so exhausted that I was on the very edge of sickness.

‘You’ll sleep well tonight,’ Fred said.

And that would normally have been true. But when we were back at the loft and Scout was brushing her teeth as I turned down the lights, Stan watched me with his huge adoring eyes, certain that the coming weekend held nothing but fun for us, certain that I would never betray him, his love and trust so unquestioning that it filled me with shame.

I crawled into bed weak with exhaustion.

And I still couldn’t sleep.

In the morning Stan was sick.

Elaborately sick at both ends. Extravagantly sick. His cage was a mess of bodily fluid that had erupted from everywhere it could. Foul liquid stuck to his basket, his blanket and his magnificent fur. Stan laid stock still in a puddle of watery filth, staring with numb disbelief at Scout and I, unable to understand what had happened during the night.

We put him in the bath and cleaned him up. Then, when most of the mess had been washed away, and he was starting to get his natural biscuit-smell back, I called the vet’s.

‘Oh, poor old Stan,’ said the kindly receptionist at the Well Animal Clinic. ‘Probably something he ate. Best leave the surgery for another day.’

Scout was fussing over him in the bathtub. The projectile vomiting and volcanic diarrhoea had left him bewildered. He looked forlorn, and half his usual size, with his fur sopping wet. But he watched me grinning in the doorway of the bathroom and a familiar, fun-loving glint suddenly lit up those eyes like black marbles.

Hampstead Heath was waiting for us.

*  *  *

Even in September, they were still swimming in the mixed bathing pond.

We saw the distant bathing figures laughing at the cold as we cut across the great rolling expanse of Pryor’s Field, Stan hanging back to hunt small flying creatures in the long grass, then sprinting to catch up when Scout called his name. Then we were in the thick forest that separates the bathing ponds from the highest point on Hampstead Heath, and Scout kept Stan closer now. A young fox stalked across our path, checked us out and in an instant was gone. We pushed on, the ground always rising, and suddenly we came out of the trees and onto Parliament Hill, blue sky all around and the city spread out below us, a sight to steal your breath away, and it was as if London belonged to us.

My phone began to vibrate.