When blood is fresh, still oozing from living tissue, it has the iron tang of a park railing just after it’s rained. Clean, slightly salty, metallic.

But the longer it’s out of the body, the muskier it becomes, acquiring the odour of everything it comes into contact with: sweat, decay, death. Sometimes I can still smell it beneath my fingernails, even after I’ve scrubbed my hands raw.

It’s astonishing what blood does. There’s no substitute for it: it can’t be made or manufactured. Red blood cells disperse oxygen and nutrients to your lungs and tissues. White blood cells carry antibodies throughout the body to fight infection. Platelets help the blood clot when you’re injured by gathering at the site and sticking to the lining of an injured blood vessel. Plasma transports blood cells throughout the body, along with nutrients, waste, hormones, and proteins that help maintain the body’s fluid balance.

An adult female has approximately nine pints of blood in her body. If she loses more than three of them, she’ll go into haemorrhagic shock, and die.

My fingers tingle as I spread my left hand against the pale expanse of exposed skin, widening the space between my thumb and forefinger to keep the flesh taut.

There’s a purity to this moment, in the seconds before I cut.

I savour the weight of the knife in my hand.

And then I slice. Without hesitation: through the epidermis, the top layer of her skin, through the thicker dermis, and on through the yellow wedge of subcutaneous fat she’s spent years trying to diet away.

Her blood flows over my fingers, bright red, oxygenated, obscuring my field of vision. It doesn’t matter: I could close my eyes, and still know where to cut. I have an almost supernatural intuition, as if my fingers can see, as if those red blood cells and platelets and plasma are communicating directly with my own blood, conveying messages along a sanguinary highway.

I only stop when I see white bone.

The heart is protected by the sternum, the organ’s skeletal armour and the central bone to which ribs are attached. Cracking it with a saw requires pressure, power, and precision. Death is measured in millimetres.

But I’m good at what I do.

Once the sternum is bisected, I use a retractor to spread the two broken halves.

And then there it is before me.

Her beating heart.

The cavity is quickly filling with blood. She’ll be dead in minutes, but I’m not going to wait that long. I’m going to stop her heart now. I inject a solution containing potassium ion directly into the aortic root. As her heart quiets, mine beats faster.