Robinson has done the right thing by old people everywhere and lost her Gold Opal card. She’s reinforced the stereotype. She’s the mad old woman on the bus, except she’s no longer on the bus.

For those who don’t live in Sydney, a Gold Opal lets you use public transport all day long for $2.50. You can catch a train to the Blue Mountains, or a ferry to the Opera House, or a bus to dreary work and back.

To qualify, you must be over 60 and magnificent. Robinson ticks both of these boxes.

We were heading out on Saturday afternoon to a friend’s exhibition at a gallery in Ultimo. We also planned to visit the fish market and take the light rail home with some trout fillets and a seaweed salad.

Robinson can’t find her Gold Opal. I find her glasses so she can look properly. The breezy early annoyance, ‘where did I put it?’, segues into ‘when did I last use it?’. We can’t remember, of course. We need a pen and paper to figure that out, and our scribbled wall calendar. No time for that now.

Robinson uses her credit card to pay full price on the way home from the fish market and fumes like an 1860s steam train.

Then the search begins in earnest. Nina The Cat senses static in the air and races up and down the corridor, thrilled, does parkour off the couch at full speed, crouches with us to look low, tail twitching, then she finds a stale pistachio nutcase and carries it out to the sunroom to crack. She can carry a ping pong ball in her mouth. She is well capable of tapping a Gold Opal onto the floor and knocking out of sight. She loves doing that shit.

‘It must be somewhere,’ Robinson declares, not very helpfully.

‘Matter can be neither created nor destroyed,’ I recite from the depths of my high school ignorance. ‘Although it can fall out of your pocket onto a footpath.’

We wracked our wrecked brains on when Robinson last used the card. We consulted the calendar scribble. Indecipherable, mostly, but… we went out for a friend’s birthday on Friday 1 July. We caught the bus. Robinson wore her red coat! She looks in the pockets. No card there. I wore a blue jacket! Not there. Not in any of her bags either, not even the one she took to the restaurant.

I give up, but Robinson starts looking in unlikely, impossible places. She finds her winter pyjamas!

We’re stranded. Well, she is, but like most things, we’re in this together. So we walked over to Newtown yesterday, in between downpours, and met up with old friends we hadn’t seen for years. They had all their beautiful kids in tow and those years just fell away. We talked family and music and politics and sport in the Newtown Hotel. The kids went exploring. The future loomed brightly.

Today, on the couch, Robinson admitted Opal defeat and checked her card online. No-one has been using it. Not even a nurse or a barista who deserve very cheap transport. She tried to cancel the card and order a new one. Needless to say, it didn’t work. Needless to say, it’s not our old, stupid fault.

Maybe we can start driving everywhere in our new car. Does anyone want my Gold Opal?