It's mid-afternoon when the fabulously named Purple Tse, our insurance fixer, confirms that we will be leaving Hong Kong tonight.

Packing takes us all of 10 minutes and Zac, on reflex, swings his pack on to his back.

"Can you take that off?" I say.

"Why?" he asks. "It's fine. And I'm supposed to use my arm."

"It's just ..." I say, thinking of the chauffeur-driven car that awaits us. "It's just you're being evac-ed to London with a broken arm. Would you mind looking a little more ... damaged?"

It's after midnight when we leave the glitter and life of Hong Kong International on an Airbus A380; it's 5am local time when we hit the sterile glitz of Dubai; and then it's Gatwick, and noon, and long, ugly immigration queues and WH Smith.

Gah! Of all the places in which to re-enter a city that once was home, Gatwick sucks.

And, further, it's having a long-overdue facelift, which means the map of Gatwick in the back of my brain no longer functions.

Somehow, we make it to London Bridge, where the grimy old bus garage out the back has been replaced by a shiny new plaza with a tonne of glass.

"What in god's name is that?" I ask Zac, accusingly. He was last in London more recently than I.

"That, Mum," my spawn replies, "is The Shard."

It's been a year since Zac last saw Fred, the friend he calls his "brother from another mother", but he has changed rather less than freshly painted post-Olympics London and – never a given – the boys have grown at approximately the same rate.

By midnight Hong Kong time, Fred, Zac and another old mate, Aslan, are playing rounders in the street; by 4am Hong Kong time, we're eating pizza in Stoke Newington and planning a sleepover. It is, as the south-east Asian T-shirts have it, "same-same but different".

A train to Norfolk – where Zac's buddy Archie is now 14 (!) and a foot taller than him and Zac is comparing surgery with his grandmother, who's also had some metal added to her person since we last saw her.

The concept of home is a difficult one when you travel long term, a complex alchemy of familiarity, friendship and memory. But London and Norfolk sit alongside Ubud, Dahab, Harbin and (for Zac) Brisbane as places that feel like home. With the sun shining, it is, for me at least, an unconflicted but firmly temporary pleasure.