Dr. Catherine Harkup

This way of tracking the sale of highly dangerous substances, it's not exactly watertight.

If you're OK with killing people, you are OK with lying on a poison register and signing the wrong name and giving the wrong address or the wrong purpose for your purchase.

So, yeah, I mean, it was a step in the right direction, but I really don't think it hindered many people.

So she was very up to date with this.

And it was interesting that poisons that she might have used at the beginning of her career were less relevant later on.

So you couldn't just drop arsenic into the soup when she was writing in the late 60s because it wasn't that easy to get hold of.

Whereas in the 1920s, it was frighteningly everywhere.

She almost never bent the rules regarding chemistry or science, which is an astonishing fate.

And she is, I think, actually a remarkable science communicator because she can put across very accurate science in a very accessible, easy way that people just digest readily.

So she's under no obligation, no crime writer is under any obligation to stick to the facts.

This is fiction.

You can make things up as you wish.

But the fact that she almost never did

I think, is to her enormous credit.

And I realise that there's very, very few people like me who appreciate that.

But it makes it so much nicer when we read a book and realise that, oh my God, they did their homework.

Oh my God, this is really how it could happen.