But that nagging little voice at the back of your head, your conscience, makes you shy away from the very idea almost as soon as it takes shape.

Honestly, I don’t know how you neuro-typicals manage. It must be like having tinnitus or one of those ear-worm songs you can’t get out of your head.

But when you watch a slasher movie, or read a novel about a serial killer, you finally get to indulge the greedy, voyeuristic parts of your soul you like to pretend aren’t there.

And you know what? It’s good for you.

Seriously. A nice juicy murder-by-proxy gives you a hearty adrenaline rush from the comfort of your own home. It’s the same buzz you get when you ride a roller-coaster.

It’s evolution looking out for you. Back on the plains of the Serengeti, you needed to kick things into high gear the moment you sensed a threat. So your body would release adrenaline, which increased your heart rate and respiration and sent oxygen and energy to your muscles to ready you for fight or flight.

These days we don’t often have to worry about sabre-toothed tigers or sharks or poisonous vipers – well, not unless we go into politics.

[Laughter]

The stresses we face are whether we can make the rent this month, or if we’re going to hang onto our job.

But our bodies haven’t evolved to keep up and so they still go into adrenal overdrive if we perceive a threat, real or not. Your survival instinct isn’t able to do what it was designed to. Which means now and again we need to give our bodies a reboot and really feel the fear.

That’s why you enjoy stories about serial killers. It’s not because you’re sick people. You’re wired to feel this way. It’s natural to experience a vicarious close call and, well, survive.

Why am I telling you all this?

Because I want you to know it’s OK that you’re getting off just a little bit by being in this room with me. It’s even OK for you to like me. I won’t tell.

[Laughter]

I told you, I’m one of the good ones. If I do something bad you can be sure it’s for a very good reason.

Sometimes you have to cut out a cancer to save the patient.

Don’t think about the lives I took.

Think about the ones I saved.

chapter 27

millie

I always sleep well: one of the benefits of being a doctor and years of working on-call. But Tom and the children know not to wake me before my alarm goes off when I’m operating the next day: the house had better be burning to the ground if you’re going to disturb me.

So when Tom shakes me awake in the grey light of dawn, I know it’s serious.