At 17:02 the children are taken out through the west gate

At 17:02 the children at the Arenillas school come out through the west gate, which is never used because it opens onto waste ground. They come out two by two, holding hands, puzzled, because it is the first time all year. The back playground, the one with a handball court painted on the concrete, has nobody in it. Above the playground, level with the fourth floor of the building next door, two local police officers are looking up with their hands on their belts, and one of them is pointing. One of the two officers is talking on the car radio and the other has run site tape between two lampposts, twelve metres of pavement, so that nobody walks under the scaffold. The after-school club leader, Nerea, counts them on the pavement: twenty-two.

At 17:00 Nerea has counted twenty-two heads in the corridor, before they go out. They have changed her gate halfway through the year and nobody has explained why.

At 16:58 the green netting on the north façade scaffold swells and falls back with the gusts. The two fourth-floor anchors are loose: two bolts in plain sight, one with the nut halfway down the thread. An anchor is what holds the scaffold against the façade; without the two on that floor, the frame works as a cantilever. The tube pulls twelve centimetres away from the wall and comes back.

At 16:55 Ximena Orbaiz, site manager, hangs up the phone in the hut and crosses out a line in the daily report. The concrete plant is taking back the four hundred litres still in the truck. Tomorrow they will have to chip the ring-beam joint — the concrete belt that closes the floor along the top — and leave it dry for the splice: a morning with a breaker, two labourers and the structural engineer, the one who signs that the structure holds, standing over them. She writes it down, puts the time on it and does not argue with herself about it.

At 16:50 Odón goes down the hundred and seventy-two rungs of the crane and it takes him nine minutes. At the bottom, Ximena is leaning on the plot fence, looking up at the scaffold next door and not at her own site.

"Since when could you see it?"

"Since four. But until the netting swelled I didn't know that was what it was."

At 16:38 Odón Berganza, fifty-eight-year-old crane operator, reads seventy-six on the anemometer at the end of the jib. The machine's manual says seventy-two. He releases the slew brake, leaves the load at zero, takes the hook up, and the crane starts to turn on its own, looking for the wind like a weathervane, which is what it is supposed to do. From up there he can see the playground without a child in it.

At 16:31 Ximena has called the school. She spoke to Teófilo Vicario, caretaker, who has the key to the west gate and who has spent eleven years asking for it to be used for something. Teófilo did not ask why: he said "give me ten minutes" and went to fetch the key, which is in the boiler cupboard on a ring with a label reading WEST (DO NOT OPEN), written by him in 2015. Then she called the local police. She did not call the site next door, because the number on their hoarding belongs to an office that closed in March.

At 16:26 Odón is thirty-eight metres up with four hundred litres of concrete hanging at a thirty-two-metre radius, and he is the only one of the twenty-six workers on sector 3 who can see the north façade of the neighbouring building. He says so over channel 4, with the bucket in the air:

"Ximena, don't put anybody on that loading platform. And write this down, because I can't show it to you from here: the scaffold next door has the fourth-floor anchors loose and the netting is swollen like a sail. And there is a school playground underneath."

At 16:19 Odón asks to stop in writing. He says it formally, so that it gets written down: I am stopping the pour and putting the machine in weathervane. Sixty-six up here, he says. The site's weather station, four metres off the ground, reads sixty-one.

At 16:10 Ximena does not let him stop. She repeats over the channel, with the time and the name, that the manager of the developer Pedregal Sur orders the pour to continue until the truck is empty. It is what she has just been told on the phone and she says it exactly as it came.

At 16:08 the real argument lasts two minutes and it is about numbers. Her: the truck mixed at fifteen twenty-one, concrete has ninety minutes from mixing, at sixteen fifty-one it is rubble, and if eleven metres of ring beam go unpoured the joint is left half done. Him: four hundred litres at a thirty-two-metre radius with the jib facing into the wind, and the load chart is not the problem, because the chart gives one thousand four hundred kilos and the load is one thousand one hundred and forty. The problem is that the wind shoves sideways and the slew, with the wind head on, arrives late.

"Then you lower the bucket," he says to her.

"Odón."

"I mean it. I'm not lowering it happily, and I want you to know that before I lower it for you."

At 16:02 Ximena opens channel 4 and asks Odón what the anemometer is reading. Fifty-four in gusts, he says. The average is running at forty-one.

At 15:50 the concrete pump blows a hose and the pump operator drives off to Nájera with the truck. There is no other pump inside forty kilometres. What was going to be a six-minute half-pour becomes five four-hundred-litre buckets hanging from Odón's crane, one at a time.

At 15:30 the reason that ring beam had to be closed today and not tomorrow fits in one line of the daily report and Ximena had written it that morning: the structural engineer comes by on Monday at nine to sign off the slab for the floor above, and with the joint half done he signs off nothing. Three days of standstill for eleven metres of concrete.

At 15:21 the truck mixes at the plant. From that minute on, the ninety start counting.

At 14:20, at the Arenillas school, the Thursday handball club lists twenty-two children aged eight to ten, from five to six in the afternoon, in the back playground. The sheet has been pinned to the board in the entrance hall since September and is signed by the parents' association. Nobody from the sector 3 site has ever seen it.

At 13:45 the national weather agency signs the yellow warning: gusts of up to eighty in the valley from five o'clock. The warning reaches the site's inbox at thirteen forty-eight. At thirteen forty-eight Odón is eating lunch in the cab, with his phone in his trouser pocket and no signal, because up there there is none.

At 12:40 Odón signs the crane logbook in the hut. He notes, as he does every day, the time he went up, the wind at that moment — eighteen — and a column headed "remarks", in which he never writes anything. He puts on his harness to climb. It is a hundred and seventy-two rungs and he goes up slowly, stopping on the third platform, because fourteen years ago they put two screws in one of his knees.

At 12:38, on the pavement, between the sector 3 site and the building next door, Odón passes the scaffolder from the neighbouring job, a man from Bilbao whom everyone calls Patxi and whose surname is Olabarri. He is loading tubes into a van that he has double-parked with the hazards on, and he has half an hour left before he goes.

"Off already?" Odón says to him.

"First thing tomorrow I am going up to tighten the fourth-floor ones. Today I have not got the time."