New Year’s Day was big and blue and freezing cold. The single shot from the block of flats ripped the day apart.

I threw myself down behind the nearest car, hitting the ground hard, my palms studding with gravel, my face slick with sweat that had nothing to do with the weather.

Every gunshot is fired in anger. This one was full of murder. It cracked open the cloudless sky and left no space inside me for anything but raw terror. For long moments I lay very still, trying to get my breath back. Then I got up off my knees, pressing my back hard against the bright blue and yellow of an Armed Response Vehicle. My heart was hammering but my breathing was coming back.

I looked around.

SCO19 were already on their feet, staring up at the flats in their PASGT combat helmets, black leather gloves hefting Heckler & Koch assault rifles. Among them there were uniformed officers and plain-clothes detectives like me. All of us keeping our bodies tucked behind the ARVs and the green-and-yellow Rapid Response Vehicles. Glock 9mm pistols were slipped from thigh holsters.

Close by, I heard a woman curse. She was small, blonde, somewhere in her late thirties. Young but not a kid. DCI Pat Whitestone. My boss. She was wearing a sweater with a reindeer on it. A Christmas present. Nobody chooses to own a reindeer jumper. Her son, I thought. The kid’s idea of a joke. She pushed her spectacles further up her nose.

‘Officer down!’ she shouted. ‘Gut wound!’

I looked out from behind the car and I saw the uniformed officer lying on her back in the middle of the street, calling for help. Clutching her belly. Crying out to the perfect blue sky.

‘Please God . . . please Jesus . . .’

How long since the shot? Thirty seconds? That’s a long time with a bullet in your gut. That’s a lifetime.

There is a reason why most gut-shot wounds are fatal but most gut-stab wounds are not. A blade inflicts its damage to one confined area, but a bullet rattles around, destroying everything that gets in its way. If a knife misses an artery and the bowel, and they can get you to an anaesthesiologist and a surgeon fast enough, and if you can avoid infection – even though most villains are not considerate enough to sterilise their knives before they stab you – then you have a good chance of surviving.

But a bullet to the gut is catastrophic for the body. Bullets clatter around in that microsecond, annihilating multiple organs. The small intestine, the lower intestine, the liver, the spleen and, worst of all, the aorta, the main artery, from which all the other arteries flow. Rip the aorta and you bleed out fast.

Take a knife wound to the gut and, unless you are very unlucky, you will go home to your family. Take a bullet in the gut and you will probably never see them again, no matter what the rest of your luck is like.

A knife wound to the gut and you call for help. A bullet in the gut and you call for God.

I heard another muttered curse and then Whitestone was up and running towards the officer in the road, a small woman in a reindeer jumper, bent almost double, the tip of an index finger pressed against the bridge of her glasses.

I took in a breath and I went after her, my head down, every muscle in my body steeled for the second shot.

We crouched beside the fallen officer, Whitestone applying direct pressure to the wound, her hands on the officer’s stomach, trying to stem the blood.

My mind scrambled to remember the five critical factors for treating a bullet wound. A, B, C, D, E, they tell you in training. Check Airways, Breathing, Circulation, Disability – meaning damage to the spinal cord or neck – and Exposure – meaning look for the exit wound, and check to see if there are other wounds. But we were already beyond all of that. The blood flowed and stained the officer’s jacket a darker blue. I saw the stain grow black.

‘Stay with us, darling,’ Whitestone said, her voice soft and gentle, like a mother to a child, her hands pressing down hard, already covered with blood.

The officer was very young. One of those idealistic young kids who join the Met to make the world a better place.

Her face was drained white by shock.

Shock from the loss of blood, shock from the trauma of the gunshot. I noticed a small engagement  ring on the third finger of her left hand.

She died with an audible gasp and a bubble of blood. I saw Whitestone’s eyes shine with tears and her mouth set in a line of pure fury.

We looked up at the balcony. And the man was there.

The man who had decided at some point on New Year’s Day that he was going to kill his entire family. That’s  what the call to 999 had said. That was his plan. That’s what the neighbour heard him screaming through the wall before the neighbour gathered up his own family and ran for his life.

The man on the balcony was holding his rifle. Some kind of black hunting rifle. There was a laser light on it, a sharp green light for sighting that was the same bright fuzzy colour as Luke Skywalker’s light sabre. It looked like a toy. But it wasn’t a toy. I saw the green light trace across the ground – the grass in front of the flats, the tarmac of the road – and stop when it reached us.

We were not moving. Everything had stopped. The light settled on me, and then on Whitestone. As if it could not decide between us.

‘She’s gone, Pat,’ I said.

‘I know,’ Whitestone said.

She looked back at the vehicles with their bright markings, the blocks of blue and yellow of the ARVs and the green and yellow of the RRVs. Between them I could see the dull metallic  sheen on Glocks and Heckler & Kochs, the medieval curve of the combat helmets, the faces drawn tight with adrenaline.

Whitestone was shouting something at them. The green laser sight on the black hunting rifle played across the reindeer on her sweater and settled there.

‘Put him down!’ she said. Then I heard their voices.

‘I have the trigger!’ somebody said. But there was no shot.

And I thought of the palaver that came with every discharged firearm. The automatic suspension and then every shot endlessly analysed, pored over, suspected. The prospect of jail and the dole queue. No wonder they were scared to shoot.

But this was not the reason for holding fire.

When I looked back at the balcony I saw that the man was no longer alone. A woman was with him. She was wearing some kind of headscarf, although from this distance I could not tell if it was faith or fashion.

He was calling her names. He was calling her all the names that kind of man always call women. Then he seemed to shove her back and pick up something from the ground. Holding it by the scruff of the neck. Shaking it.

A child. A toddler of two or less. From where we were kneeling  with the dead officer  I could see the chubby look that they all get at that age. The kid squirmed like a tortured animal as the man held it over the edge of the balcony.

Four floors up.

Nothing but concrete below.

The man was shouting something. The woman was weeping by his side and without looking at her he struck her in the face with the butt of the black hunting rifle. She stumbled backwards.

Then the child was suddenly falling. The woman screamed.

‘Take the shot!’ someone shouted.

There was a single crack that sounded very close to the back of my head and immediately a spurt of blood came from a hole in the neck of the man on the balcony. He did not fall. He staggered backwards and smashed through the glass window behind the balcony, and as he disappeared from view I thought how fragile we all are, how very easy to break, how always so close to ruin.

And then I was running, my shoes slipping on grass slick with ice, the call for God’s help coming unbidden from my lips, holding out my arms for the falling child.

But the distance between us was too great, and there was never enough time, and the child was always falling.