Marc Fennell

There is a man hurrying down the street, his eyes fixed ahead and his coat swinging as his feet hit the pavement.

As a train whistle sounds, steam rises and in the shadows, someone is watching.

As he sits down, his heart thumps.

He breathes deep because he's made it.

He has outrun his past.

Except little does he know that his past isn't behind him at all.

In fact, it's racing alongside him.

We'll wait for him at the next station, all thanks to a futuristic machine.

I'm Marc Fennell, and this is the story of a murder and a strange new technology that helped catch a killer before anyone really understood what it could do.

A machine that would go on to change the world, but at the time, no one saw it coming.

So let's start with this.

Happy New Year.

It is the 1st of January, 1845.

And right now you're in front of an unassuming row of cottages in Slough, which is about an hour west of London.

This is Ryder, a cultural historian and good friend of the show, Cassie Sinclair.

When Sarah's body goes still and her screams stop, a silence falls on the house.

The doctors and neighbors look around to see what could possibly have caused her this agony.

And then they notice something on the table.

Because it turns out that something was put in that beer that definitely should not have been there.

Now, prussic acid, you might know it by its more familiar name, hydrogen cyanide, which, if you've ever read Agatha Christie, is never a great sign.