‘No shoes, Lissa. If you get them dirty, they’ll know you’ve been out.’

Mrs Melissa Penworthy slides open her sash window to the cool night air and the distant rumble of traffic, her breathing laboured from the effort. She looks around for a handbag to take with her. Where do they all go? This one will have to do.

She often talks to herself these days, and no longer cares who hears or doesn’t. Much the best way to enjoy a civilised conversation. Why waste words on those ghastly care workers? Their patronising smiles don’t fool her; she knows they hide her handbags when she’s not looking. They do it deliberately to confuse her. As for her children, all middle-aged spread and interfering advice... well, she won’t give them the satisfaction. On and on they prattle when they visit, trying to jog memories about people and places she’s never heard of.

‘Mum, you remember…’

There it is again: that concerned frown she sees puckering everyone’s brow. No, she doesn’t remember, and at her age, why should she?

‘Look at this, Mum.’

Fat fingers poke at buttons and thrust tiny screens under her nose. No, she doesn’t care to squint and admire. She’s not sure which is worse: strangers who treat her with the familiarity of family, or relatives whose ways feel utterly foreign.

‘Enough is enough. Time to call the cavalry.’

Mrs Penworthy’s toes, released from their cushioned slippers, wiggle in anticipation. She settles her hips on the window sill and pulls the cord of her ancient dressing gown tighter, bolstering her thickened middle and her spirits.

‘Gemma will help. She’ll make them all see sense. Then I can go home.’

Gemma is Mrs Penworthy’s eldest granddaughter and, by anyone’s standards, a clever girl. Brains must have skipped a generation. Gemma’s letters, thoughtfully printed in large type, share anecdotes about her work as a scientist in America. Her grandmother doesn’t fully understand what Gemma does or why, but she knows it involves looking after a robot whose job is to explore the surface of Mars, and she couldn’t be more proud.

She always writes back, and this time she’s told Gemma how the rest of the family have hoodwinked her.

‘Just for a few weeks’, they’d lied. ‘Respite care for you, and a break for us. See how you get on. You might like it.’

How long ago was that? Certainly weeks, possibly months.

Mrs Penworthy hoists her bare toes up onto the window sill, inching them over the rough sandstone and out into the silky darkness. It’s chilly out there, but bearable. What a relief she’d insisted on a ground floor room. Imagine the horror of being trapped upstairs. She might still feel twenty five inside, but her days of shinning down drain pipes are long gone. She tucks the letter to Gemma into her handbag and…

‘One, two, three.’

…lands on the soft earth between the roses.

She steadies herself against the wall and inhales deeply, filling her lungs with black oxygen and the honeyed fragrance of the floribundas. Her eyes adjust and carefully she tilts her head back to marvel at the distant scattering of diamonds across dark velvet. Somewhere up there a little robot is beating a lonely path. She knows it’s just a collection of man-made parts, but feels an emotional pull nevertheless.

‘If you can keep going, so can I.’

She picks her way along the stone flags to the old wrought iron gate in the corner of the garden. The latch is rusty and squeaks, but allows her through. The smooth pavement beyond is easier to walk on and the street lamps cast guiding pools of light. At the end of the road she pauses, peering around the junction. Is it left or right to the post box? It’s been a while and the landscape feels unfamiliar.

‘Try left, Lissy.’ If she talks to herself confidently, all will be well.

Stepping sensibly between the cracks in the paving, Melissa Penworthy recalls her granddaughter’s descriptions of the robot’s adventures up on Mars. It has photographed rocks, explored craters and trundled hundreds of miles to collect data for scientists back home. Designed with a life expectancy of just three months, its persistence has astonished its creators, and long past retirement age it’s still stoically exploring the strange red planet. Such a shame it hasn’t found any little green men to talk to.

The robot suffers regular hardships. Gemma has told her grandmother about sandstorms that scour its solar panels, harsh winters that force it into hibernation to conserve power and the time its wheels lost grip on the red dust and spent hours trying to move forward, only digging itself deeper. The scientists had put their brains together and come to the robot’s rescue, explaining from afar how to reverse out of the pickle. They couldn’t fix its broken front wheel or prop up its drooping arm, but it had emerged sufficiently intact to fight another Martian day.

Mrs Penworthy sympathises with the robot’s plight in handwriting that becomes wobblier each time. She can tell from Gemma’s letters that her own don’t always seem to arrive safely. So frustrating, and she can’t work out why.

A bus shelter looms into view, plastic windows plastered with tatty posters. There’s a bench underneath and she sits for a moment to rest her feet, smoothing the drape of her dressing gown over her knees.

She knows she’s been here before, but can’t quite remember what it’s called. Night time changes the look and feel of a place, just as sunshine transforms it. She can see a row of shuttered shop fronts glowing amber beneath the sodium street lights. In front of them, swirls of dust dance along the white line down the middle of the empty tarmac. She lifts her dusty toes into the light and admires their orange hue. She really shouldn’t have come out without wearing shoes, that was silly. She must have left home in a hurry. What could have been so urgent that she would rush outside in the middle of the night with bare feet? And why did she bring her old green crocodile handbag instead of her shiny new black one? She flips the bag’s silver clasp with a practised hand and searches inside for clues. Bus pass, yes, glasses case, yes and what’s this? She pulls out a stack of letters, some crisp and new, others dog-eared and tatty. The handwriting is smudged, but it looks like her own, so they must be waiting to be posted. Nothing useful there then.

‘Take your time, Lissa. You can work this out.’

As Melissa Penworthy tries to marshal her thoughts, she leans her against the window of the bus shelter and lets it loll. Gradually her eyes droop and sleep steals a hold.

Dreams fly her up to Mars, where she meets the ageing robot. It’s wearing itself out, repeatedly trying and failing to plough through a deep drift of fine red dust. As if teaching a toddler to walk, Mrs Penworthy takes the little robot by its damaged arm and gently helps it back out to firmer ground, all the while murmuring soothing nothings. Once the robot can move freely, the two set off together, hand in hand, to explore the vast red planet. They collect rock samples, take photographs of the alien landscape and share stories of spirit and opportunity. They’ll send all these back to Gemma, far away on the beautiful blue planet hanging low over the horizon.

Back on Earth, the paleness of dawn unites with a cool morning breeze to nudge Mrs Penworthy awake. Her hips have stiffened and she can barely feel her feet, but the doze has recharged her batteries. Her surroundings slide into focus. The row of shops looks more familiar in the early light and just beyond the bus stop sits a bright red post box.

A post box. Of course. What a brilliant idea; she should write a letter to her granddaughter in America and ask her to intervene in the care home situation. Why didn’t she think of it before? If the clever girl could keep a robot safe on Mars, she should be able to protect her old grandmother just a continent away.

Mrs Penworthy grips the side of the bus shelter, pulls herself onto her grimy feet and sets off for the care home. No time to sit around here admiring the scenery; there’s a letter to write and post. She’d better put shoes on too, before anyone thinks she’s becoming forgetful.