Late evening, and Joan is in the kitchen washing up her cup.
There is a pause as the darkness descends. A surprised silence and only the sound of the water running.
"I have a torch, Watson," calls out Sherlock, appearing in the kitchen with a flashlight. Its yellowish glow sends eerie shadows spidering across his face.
Joan stands still at the sink, hands under the running tap, remembers to turn it off. "Is it just us?" The brownstone has ancient wiring. Only the parts required to maintain Sherlock's high tech hobbies have been renewed. Less vital aspects - heating, stove, lighting - are probably a hundred years old.
"No, the whole street. I'm going up to check the bees, want to come?" He is dancing from toe to toe in T shirt and scruffy jeans.
"No, I'm good, thanks. I'll look for candles."
"We haven't got any," he says casually, leaving the kitchen, and her in darkness. "They're a fire hazard!" he calls back, haring up the stairs.
She sighs. Ask him if there is milk, and he has no idea. But of course he knows immediately that candles do not exist in the house. He probably used them in some experiment which required hot wax.
In the dark, hands dripping as she fumbled for the towel, Joan has an instant thought of an activity which might require hot wax. Startles herself - she generally tries not to think about Sherlock's sex life, even when a girl in obvious professional gear turns up with a bag which clanks ominously- but accepts that it is indeed a possible reason why he knows there are no candles.
Ok, rational thought now. Dry hands. The kitchen is dark and Sherlock is on the roof with the only known source of light.
She steps cautiously into the living room. All TVs off, a very faint glow from the IPad, running on battery. Thinking this, she takes her phone out of her pocket and uses its dim blue light to navigate the room, figuring it is worth checking the breakers anyway in case Sherlock is wrong about it being a general power cut.
"There's a torch app on your phone - but better not use it as it runs down the battery," Sherlock says, close behind her.
She jumps. He has crept in, silent as a cat, the flashlight switched off.
"Conserving power," he says, as if he can see her glance at the unused torch. "Don't know when we're going to get a chance to charge it up again."
"What? When the power comes back on, presumably."
"I have a rather pessimistic feeling about that. Come and look."
He reaches out, finds her hand, wraps his calloused palm around hers. "The eyes adjust surprisingly quickly to low light levels," he says. "It has been less than six minutes and already I can make out your face quite clearly."
She rolls her eyes as he leads her up the stairs. Trust him to start cataloguing blackout phenomena.
"For example, you just rolled your eyes," he says, ahead of her.
"You have your back to me."
"I felt the gesture through your fingers. You clenched. There are many ways of seeing, Watson, of perceiving, of knowing." He is gleeful.
It is no surprise to disover that Sherlock relishes a crisis, even a mundane one like a power outage.
They reach the roof. "Mind the apiary," says Sherlock and guides Joan around the various vents and skylights making lumps in the flat roof.
They stand at the parapet.
New York is dark.
"It's not just our block," breathes Sherlock. He is leaning forward, drinking it in, the strangeness of seeing their city without lights. "It's everywhere."
Joan sees twinkles in the sky - planes circling over the airport, unable to land. She wonders what they do when the power goes at air traffic control. They must have generators. Like at the hospitals.
It is very dark without even streetlights. There is noise, raw noise, people only noise, sharp and undamped by the normal background hum of the city.
Cars' engines are individually audible as they pass.
"Look how people turn their faces towards the headlights," says Sherlock, pointing. Some people along the street have come outside and are standing looking around, uncertain, no plan now that the tv and computers are off. Their faces are lit briefly as a car passes. "A natural human impulse, to seek out the light."
When there are no cars in the street, it is hard to see the people there at all.
Joan shivers. "I hope this doesn't last too long," she says.
Sherlock laughs, sweeps his arm around to indicate the horizon. "Look at it, Watson. The whole of New York is without power. It will take them a while to fix this."
She feels him take her hand again, the movement sure and quick. "Want to go for a walk?"
"In the city? In total darkness?" She thinks: danger, looting, crime. Misrule.
Sherlock lives for misrule. "Of course!" He grabs her shoulders, swings her round and round. "Adventure, Watson! Anything could happen. And anyway, it won't be in total darkness. We have a torch."