The blood is everywhere. It spurts uncontrollably from Melissa’s neck, covering her desk and turning her shirt crimson. The fingers on her right hand spring open, and the knife she was holding clatters to the floor.

I start to shake. I look down and realise I, too, am covered in blood. My own knife is still gripped tightly in my right fist, but the adrenaline I felt when I stabbed her has passed, leaving me dizzy and disorientated. If she comes at me now, I think, I won’t be able to stop her. I have nothing left. I reach down and with my free hand I pull off the duct tape from around my ankles, kicking over the chair in my haste to move away from Melissa.

I needn’t have worried. Both her hands are clamped around her throat, in a futile attempt to stem the stream of blood that pulses between her fingers and coats her hands. She opens her mouth but no sound comes out, beyond a rasping, bubbling noise which causes red foam to coat the inside of her lips. She stands, but her legs won’t comply, and she sways unsteadily as though she’s drunk.

I cover my face with my hands, realising too late that they are speckled with blood which smears across my cheeks. It forms a dull shadow on the edge of my vision and fills my nostrils with a metallic tang that makes my stomach heave.

I don’t speak. What would I say?

I’m sorry?

I’m not. I’m filled with hatred.

Enough hatred to stab the woman I thought was my friend. Enough hatred to watch her, now, fighting for breath, and not care. Enough hatred to stand by as her lips turn blue and the urgent beat of her blood slows to a quiet, imperceptible rhythm. The fluid that a moment ago was spurting feet away from her, now ebbs gently, its urgency spent. Her skin is grey; her eyes the only living thing in a dying husk. I look for remorse, or for anger, but see none. She is already dead.

When she falls it isn’t to her knees. She doesn’t stagger, or clutch at the desk in front of her like in a film, or reach out to grab me and take me down with her. She falls like a tree, crashing backwards on to the floor with a bang to her head that makes me foolishly worry it might have hurt her.

And then she’s still; hands splayed out to her sides, and her eyes wide open, bulging slightly out of her ashen face.

I’ve killed her.

It’s only now the regret sets in. Not because of the crime I’ve committed, or even because of what I’ve seen – a woman drowning in her own blood. I regret it only because now she’ll never have to face her crimes in a court. Even at the end, she’s won.

I sink to the floor, feeling as drained as though the blood had left me, too. The key to the door is in Melissa’s pocket, but I don’t want to touch her body. Even though there are no signs of life left in her – her chest does not rise, there is no death rattle as air leaves her lungs – I don’t trust her not to suddenly rise up; to grip my wrists with bloodied hands. She lies between me and the desk and I sit and wait for my body to stop shaking. In a moment I will need to step carefully around her, to dial 999 and tell them what I’ve done.

Katie. I need to tell them about Katie. They need to go to Leicester Square; I need to know if she’s still alive – she needs to know I’m okay, that I haven’t given up on her … I stand up too fast, my feet skating on the slick of blood that seems to cover the entire floor. A stripe of blood dissects the computer screen on which I can still see the CCTV image, the door to the maintenance cupboard still resolutely closed.

As I find my balance I hear the distant wail of sirens. I wait for them to die away but they grow louder, more insistent, until they hurt my ears. I hear shouting, then a crash that echoes through the house.

‘Police!’ I hear. ‘Stay where you are!’

I stay where I am. I couldn’t move even if I wanted to.

There’s a thunderous noise in the hall, and an almighty bang as the kitchen door flies open and hits the wall behind it.

‘Hands in the air!’ one of them shouts. I’m just thinking how ridiculous it is to expect Melissa to do that, when she is clearly incapacitated, when I realise they mean me. Slowly, I raise my hands. They are covered in blood, which has streaked across my arms, and my clothes are stained dark red.

The officers wear dark boiler suits and helmets with visors down and POLICE in white letters on the side. There are two at first, swiftly followed by another pair who arrive in response to the first’s clear command.

‘Support!’

The first two approach me, stopping several feet in front of me. The other pair move rapidly around the room, shouting instructions to each other. Elsewhere in the house I hear more police moving around. The sound of running feet is interspersed with cries of ‘Room clear!’ which drift down into the room in which we stand.

‘Medic!’ someone shouts. Two new officers push through and run to where Melissa is lying on the floor. One of them presses their hands against the wound in her neck. I don’t understand why they’re trying to save her life. Don’t they know? Don’t they know what she’s done? It is a pointless endeavour anyway; the life has long since left her.

‘Zoe Walker?’ It is one of the two police officers in front of me who says my name, but their helmets mean I can’t tell which one is speaking. I look from one to the other. They have positioned themselves two metres or so apart, so that as I look forward one is at ten o’clock, the other at two. In every respect they are mirror images of each other; one foot slightly forward, their hands above their waists and open-palmed; non-threatening, but ready for action. Behind them I see the medics kneeling beside Melissa. They have laid a clear plastic guard across her face and one of them is pushing measured breaths into her mouth.

‘Yes,’ I say eventually.

‘Drop the weapon.’

They’ve got it all wrong. It was Melissa who had the knife; Melissa who held the blade to my throat until the skin split. I take a step forward.

‘Drop the weapon!’ the police officer says again, louder this time. I follow his gaze, looking up to my right hand, where the silver blade gleams through its coating of blood. My fingers snap open of their own accord, as though they have only just become aware of their contents, and the knife skitters across the floor. One of the officers kicks it further away from my reach, then pushes up the visor on his helmet. He looks practically as young as my children.

I find my voice. ‘My daughter’s in danger. I need to get to Leicester Square – will you take me?’ My teeth are chattering and I bite my tongue. More blood; my own, this time. The officer looks to his colleague, who lifts his own visor. He is much older, a grey beard neatly trimmed beneath kind eyes that crinkle at the corners as he reassures me.

‘Katie’s fine. She was intercepted by one of our officers.’

The rest of my body begins to shake.

‘There’s an ambulance on its way – they’ll take you to hospital and get you sorted out, okay?’ He looks at his young colleague.

‘Shock,’ he explains, but it isn’t shock I feel, it’s relief. I look beyond the officers. A paramedic is kneeling beside Melissa, but he isn’t touching her, he’s writing something down.

‘Is she dead?’ I don’t want to leave this room until I know for sure. The paramedic looks up.

‘Yes.’

‘Thank God.’