It first appeared atop the pale-brown lip of an aristocrat, two inches across and a half-inch down and rendered luxuriantly in black strokes. Gunther was almost sure he had not seen it before and paused to look again. Lord Carrington stared stiffly back, white-wigged and red-coated and much improved for the addition.

Ian came in leading a flock of school students. Gunther beckoned him over. “Do you see anything different about Lord Carrington’s portrait?” Ian’s gaze moved from Gunther to the portrait and back to Gunther again. “They’re portraits, Gunther, not seasons. There’s never anything different about any of them.” At the other end of the hall the students were shuffling their feet and fiddling with their phones as though in support of Ian’s statement. There had never been anything different about any of the portraits. The museum would have been outraged at the notion of there being anything different about the portraits. There was in fact an incorruptible sameness to all of the portraits, with their starched collars and ruddy noses and sheep-like eyes that looked haughtily at toddler and geriatric alike, that not even the pall of time had softened into something human. Gunther resumed his patrol of the east wing and put the moustache out of his mind.

...

It next appeared on the face of a Herb Tarquin who had in life appeared to do little but exist. Gunther polished his spectacles, put them on again and stepped close enough that his nose almost grazed the canvas. He raised a finger and brushed it across the moustache, willing himself to not think that it fluttered. Duty impelled him to revisit Lord Carrington’s portrait, the upper lip of which was now as clean as a newborn’s. On a personal front he welcomed the diversion, but an inherent honesty called for the seeking of a second opinion. He summoned the museum’s art handler, a forty-something named Linda, who took the portrait to the restoration room and examined it with a magnifying glass.

“Has this painting been handled by anyone else recently?” she asked.

“Not to my knowledge,” said Gunther. “Ian and I are always around during visiting hours, and we haven’t had an art history student in a while. And we’d know if there’d been a break-in, the alarms would have tripped.”

“Hmm!” said Linda, retrieving a piece of gum from her pocket.

“So was the moustache painted recently?” Gunther prompted.

She took her time to unwrap the gum and chew it into a malleable wad before answering. “By the looks of it, no. There’s no unevenness anywhere on the surface, and the paint quality of the moustache is exactly the same as the paint on the rest of the portrait.”

“But I’m telling you, it wasn’t there until a few days ago.”

Linda shifted the gum to one side of her mouth and smirked. “Well then, it appears Mr Tarquin has gone and grown himself a moustache.”

Gunther gave her a withering glance before retrieving the portrait and exiting the room.

...

Over the next few weeks the moustache began appearing and reappearing at will, choosing portraits in no discernible sequence and remaining for two to five days on each. Gunther eyed its progress with both avid interest and a growing consciousness that something should be done about it. To eliminate the possibility of a corporeal prankster he had talked Ian into doing a night patrol of the museum. Temperatures had dropped abruptly that night and Ian had walked out the next morning in high dudgeon, informing Gunther between sneezes that he was taking the rest of the week off and was this Gunther’s idea of a joke, and news to the effect that the moustache had moved once again did not mollify him.

At its tenth reappearance Gunther approached the museum curator, who listened to his tale with visibly mounting irritation.

“A practical joke,” he said. “A vanishing ink pen maybe. Either that or you just didn’t notice it earlier.”

Gunther looked at him pityingly. “Mr Hemming, I’ve been working at this museum for ten years, I know every stroke of every painting here by heart.”

“You’re not really asking me to believe in some kind of supernatural cause, are you?”

“Why don’t you sleep over at the museum tonight and see for yourself? It’s been five days now on Lord Merton’s portrait. About time for a relocation.”

They laid out sleeping bags and dined on beef sandwiches in silence, Gunther’s anticipatory, Mr Hemming’s stony. The next morning the moustache was found on Lord Merton’s face once more.

“And how do you explain this?” said the curator with mock politeness.

“One more night, let’s give it one more night,” said Gunther hastily.

The next morning he shook Mr Hemming awake with something of triumph. Mr Hemming looked at Lord Merton’s portrait, gulped and rubbed his eyes.

“But…but it can’t be,” he said. “Where did it go?”

“Look around,” said Gunther, not entirely able to conceal a smirk, “it’ll be on one of the others.”

And it was Mr Hemming who, after several seconds, cried out: “There!”

Across the hall, upon the stately features of the late Dr King, reposed a thick black moustache.

“But what’s causing it?” said Mr Hemming, wiping his brow.

“A spirit of sorts, no doubt. Seems harmless on the whole.”

“Well, we can’t just sit here and let it happen. What are we going to do about it?”

“I’ll tell you what we’ll do,” said Gunther with a grim smile. “We’re going to talk about it.”

...

In the pre-moustache era the museum’s Instagram page featured a total of thirteen Instagram posts, the most recent of which was three months ago and all of which had to do with either holiday greetings or closures. Gunther, aided by an amused Linda, uploaded a picture of Dr Kingston’s portrait with a caption to the effect that the moustache would soon be moving to another portrait of its own volition and anyone keen on following its progress should stop by. Initial traction was low, with the few people stopping by doing so on account of a semi-popular blogger who had reshared the post with a caption that went, somewhat satirically: “Move over treasure hunts, it’s time to #FollowTheStache!” One month later another blogger, who had been stranded in town overnight after missing a bus, revisited the museum and uploaded a photo of the moustache on a different portrait with the caption “Omg this is really happening #FollowTheStache.” The blogger had a follower count of 756,000 and within hours the post had gone viral. Tourists began staying longer in town just to see the moustache move, and #FollowTheStache became the official tracker for where it was on any given day. A travel journal featured the museum on its ‘List Of Strange Things To See Before You Die’; a smartphone brand launched a giveaway based on who would capture the maximum number of moves. Footfall reached a peak, which did not entirely please the curator.

“They come here to laugh at us,” he grumbled. “We’re an art gallery, not a funhouse.”

All the same he had the prudent idea of hiking the entrance fee.

As though flattered by all the attention the moustache began switching things up, stretching its stays on each portrait to weeks on end or shrinking them to a single day or less. There was the time it spent twenty-two days on the face of Emil Dufarge, a cocoa merchant with a triple chin and a hairless head. This was followed by the day when the moustache relocated from Nelson to Napoleon in the space of two hours, causing those present to develop a mild form of mass hysteria about whether or not they had entered a wormhole. Some swore that the phenomenon would reveal the location of a secret treasure; others said that it could hold the key to confirming Riemann’s hypothesis. A sociologist collated its movement patterns and observed that the moustache had changed places a total of 85 times; the same sociologist later shared that 85% of museum art was by white people. The race angle added a fresh wave of furore and business had never been better. Gunther found himself waylaid by journalists who wanted to know what it all meant and seized the opportunity to be clever. “Well, now, I suppose it means men will be men, don’t you think?”

...

But when it made an appearance on the sylph-like features of a Madonna On The Rocks, people began to demur. Travelling moustaches were all very well, but religion was religion. The local church sent in a strongly-worded statement and the conservatives organised a protest march outside the museum. The curator approached Gunther with a frown and a sniff.

“It’s in bad taste,” he said. “Something needs to be done about it.”

“What do you want me to do?” Gunther protested. “It has a mind of its own.”

“This is a museum, not a hothouse for budding minds,” said Mr Hemming. “And anyway, it’s only paint, isn’t it?”

And, sensing that the curator had been waiting to find a scapegoat from the start and that his own involvement in the moustache’s discovery made him a prime pick, Gunther agreed without further comment that something had to be done.

...

By then almost all the portraits in the museum had had a turn. Gunther stood before Lord Milbank's portrait and eyed the moustache for an hour and thirty-seven minutes before professing himself defeated and approaching Linda for help. Linda, sympathetic, led him to the storage closet and showed him a bottle of clear liquid.

“It’s an anti-graffiti coating. It prevents paint from bonding to the surface it’s applied on. Put a bit of this on the portraits and the moustache won’t have anywhere to go.”

Gunther looked at it doubtfully.

“I wouldn’t want to mutilate the original paintings.”

“It doesn’t affect the surface below,” she said patiently. “You can remove it easily enough when you want to.”

“But do you think regular chemicals will work on something like - well, this?”

“At the very least,” Linda pointed out, “you’ll be telling the moustache it’s not wanted.”

The same evening Gunther armed himself with the coating and took up position in an anteroom. The last set of visitors came and went, Ian completed his rounds of the museum and signed out. At midnight the entrance hall clock began to chime.

“All right, whatever-you-are,” said Gunther, “let’s see how you get out of this one.”

Swiftly and silently, he used pieces of gauze to smear the coating on the upper lips of every portrait.

The next morning the moustache had vanished from Lord Milbank’s upper lip - and, as an inspection of both floors made evident, from the museum altogether.

“Bravo!” Gunther said to himself. He heard footsteps behind him and turned.

“Ah Ian, good morning. You’ll be pleased to know that I’ve solved our little problem.”

Ian raised an eyebrow.

“Looks like you have a problem of your own to deal with.”

There was a moment of silence, and then Gunther lifted his finger to his upper lip. There sat the stubbly hairs of a thick, full-grown moustache.

The ladies’ bathroom was to his left. He barged inside, almost knocking two schoolgirls over, and looked at himself in the mirror. The moustache was exactly as it had been in the paintings, black and luxuriant and two inches broad. It was outrageous. But this one he could fix. Rushing out, he bought a razor from the nearest shop and returned. With five purposeful strokes he had shaved off the moustache.

“Just a hiccup,” he said, coming back outside, “nothing to be worried about.”

“You might want to reconsider that,” said Ian coolly.

And a return to the bathroom revealed that the moustache was back. Gunther shaved it off, stepped away, urinated fitfully and looked again. The moustache was back. He shaved it off again, looked away for five seconds and looked again. There it was. Every time he took his eyes away for more than a second it would return, as bushy and black as ever.

Finally, he realised what he had to do. Taking a deep breath he shaved the moustache off. Then he dragged a stool forward and seated himself at the countertop, keeping his eyes on the mirror all the while. He allowed himself only micro-blinks where he would open his eyes before he had fully finished closing them, and every time his eyelids drooped shut he would shave the moustache off and start again. Over time he perfected the art of staying still and staring endlessly into the clean-shaven face before him. He blocked out hunger and thirst and sleep and calls of nature. He grew emaciated and his skin and bones began to stiffen. One day Ian shook his arm and found that he had turned to stone.

“Let’s make the most of this,” he suggested to Mr Hemming.

And thus a fresh fiction was spun on Instagram about how Gunther was trapping the moustache within the mirror by sheer willpower. Tourist interest began to surge again and people would pay to enter the bathroom and watch Gunther stare blankly into the mirror. This went on until an oppressed-looking teenager pushed his way to the front of the crowd. “It’s cruelty, is what it is,” he said. And he proceeded to wrap his hand in his cardigan and drive his fist into the mirror. Cracks streamed out in all directions and split the reflection into fifty. Gunther blinked, tilted his neck from side to side and raised his hand to his upper lip. The moustache was back.

“Well,” he said, “I might as well learn to live with it.”

He got up and made his way through the crowd and back home. That evening he received a letter with the museum postmark. It was a bill for the construction of a new ladies’ bathroom.

...

Years passed, the museum long returned to obscurity. Gunther grew grey and stout, but the moustache stayed as black as ever.

“I think it suits you,” said Emma, his housekeeper. “Who cares if its origins aren’t quite natural?”

“Yes,” he said, examining it once again for greys, “but I wish it would adapt a little more to a natural body. It’s not like I can start dyeing my hair now.”

One day he was on a round of the museum and stopped before the portrait of Lord Carrington, on whose face the moustache had first appeared.

“I wonder what you were trying to tell me,” he said wistfully.

The next moment he blinked. The moustache was back on Lord Carrington’s face. In growing bewilderment, he looked around at the other portraits. They had all sprouted moustaches, identical to the hair.

“What the…”

And then Lord Carrington’s portrait stirred, yawning and stretching, and the eyes swivelled round to meet Gunther’s.

"There you are," the portrait said, "took you long enough to get here, didn't it."

“What’s going on?”

“There’s a curse on this portrait,” it waved its hand. “The original Lord Carrington had a fondness for witchcraft. Went out of his depth - tried to summon an angel, got an imp instead, the shape-shifting kind. This one likes to turn into a moustache - anyone who tries to stop it from moving gets a moustache himself. I tried to myself, back when I was working at the museum. Turpentine. It’s taken about fifteen of us this way.”

“But how come you’re talking now?”

“Simple. It’s the first time you’ve come back to my portrait and spoken directly to me. That’s how the spell gets transferred to the next person. Ask and you shall receive, only the other way round, if you know what I mean. Oh well, the occult has its own rules, I suppose. And now I really must be going.”

The portrait shimmered and zig-zagged, and Gunther felt an almighty squeezing in his brain. When he regained consciousness he was apparently still in the museum, but there was something strange about where he was sitting - the portraits on the opposite wall seemed to be on a level with him. The moustaches, moreover, had disappeared. He tried to get up. His legs would not move. He looked down to see what the matter was, and as he did so he saw himself. Or rather, he saw the erstwhile Lord Carrington looking up at him, dressed in Gunther’s khaki-coloured uniform that had expanded without apparent strain to fit his lordship’s mightier girth.

“I wouldn’t worry too much,” said Lord Carrington. “Someone’s bound to figure things out the way you did. Of course, it might take a while - me, I was in there thirty-five years. But all said and done, you could be worse off. Think of all the women’s bottoms you can stare at without them noticing.” And with a quiet chuckle he walked off.

For the next several minutes Gunther evaluated his options. Mr Hemming - dead, Ian and Linda - retired. Visitors who might know him - there, two students from the local high school. He willed them with all his might to look his way, but their eyes swept over him as they did all the portraits - unseeing, uncaring.

And yet he could not feel disheartened. He had held the moustache in thrall before, in the ladies’ bathroom. He could do the opposite now if he practised hard enough.

“And I have all the time in the world to do it,” he reminded himself.

On his upper lip the moustache twitched.