Outside, on Clarence Street in downtown Sydney, it’s a grey and drizzly early winter evening, the tail end of the homeward traffic rush. Inside, behind an anonymous door and down an unremarkable flight of stairs, the canapes are circulating and the bonhomie is building among a coterie of couples with one vital asset in common.

They own second homes worth at least $3.7 million (In fact, some of them own more). And they’re here because this has given them entrée to ThirdHome, a holiday home-swapping club for the very wealthy.