♪ So far, so familiar, but how did Sherlock solve this new case?

♪ I'm restaging the crime with Jonathan Ferguson, the keeper of firearms at the Royal Armouries.

Here comes the head of Sherlock Holmes.

♪ In "The Empty House," Sherlock catches the killer, a member of Moriarty's gang, by setting a trap with a dummy of himself as bait.

I don't find that totally convincing as a head.

Do you?

I know what'll make all the difference.

That will.

There we are, absolutely unmistakable.

We know Arthur was obsessed with the latest technology, which fed into his new Sherlock stories, but I'm wondering if his science stands up to scrutiny.

Dr. Watson describes this gun that the assassin has got.

It appeared to be a stick, but it's made out of metal and he puts it together, "ending...in a powerful click."

Well, it's almost Hollywood, isn't it, sort of what we call a takedown sniper rifle today.

A takedown sniper rifle.

They wouldn't call it that then.

Something similar is this, and this is Giffard's-- or Paul Giffard, I guess, because he's French originally.

Oh, yes-- Giffard.

Yeah, and it's in all the papers-- the national papers and local papers, even-- but from 1890 to '94, when the story is set, he's set up a factory in the UK and is making and selling these.

So this is the most exciting new gun in London, and he's put something like it in the story.

Between those 4 years, it absolutely is, yes, and it's using this newfangled new gas, so it's an air weapon, we would call it, but it's CO2, or, as they called it then, carbonic acid gas.

Well, let's put Arthur to the test and see if his scenario is actually going to work-- the air rifle, Sherlock Holmes, and the window in between because they're firing across the street and through the window.

That's what makes this thing super powerful by Victorian standards, so it's got to go through a pane of glass, through someone's head, and then flatten on a wall behind.

A rifle of the period would do that.

Yeah.

Could an air rifle?

Worsley, voice-over: According to the story, when the assassin fired, there was a strange, loud whizz... [Gunshot] and a long, silvery tinkle of broken glass.

At that instant, Holmes sprang like a tiger onto the marksman's back.

To give me a fighting chance at hitting the dummy Holmes from the right distance, Jonathan has upgraded my air rifle.

Is that--that about it?

Ferguson: That'll do it.

Now, the baddie in the story was the best shot in the Eastern Empire, which meant he was always killing tigers in India.

I got it.

I got it, so, well, can I go now?

Ooh!

Ooh, straight through the window.

Look at the jelly quivering.

Oh, I got him.

I got him.

Hee.

I'll take that.