(mysterious music) In desperation, and not a moment too soon, the Americans began to devise a bold new strategy.

They were trying to get into bed with Britain's oldest enemy... France.

Benjamin Franklin, their most experienced diplomat, was sent on a top secret mission to Paris... to try to secure French support for the revolution.

Franklin had once lived in London, and been a big fan of Britain.

But now, it seems, he's become Britain's nemesis.

I've come to the archives of the Royal Society, in Central London, to take a closer look at Franklin's dramatic transformation.

(tense music) How is he today?

Meet Benjamin Franklin, in the London phase of his life.

He looks like a man who'd be, as he was, completely at home here in the Royal Society, where he enjoyed electrocuting himself in the name of scientific progress.

This is Franklin, the loyal subject of the British Empire.

But you've got to see this... This is the transformation in his appearance that happens when he goes full-on American.

When he's in Paris, representing the colonists, he's created a totally new look for himself.

He would now wear a furry hat from some North American animal.

He had a beaver one, he had a raccoon one.

And he was famous for wearing a homespun shirt.

There was nothing of the courtly or the kingly about him anymore.

He was channelling rough raw American simplicity.

I suppose what he was doing was presenting himself as the human face of this new nation in the process of being born.

(reflective music) To the French, this was extremely enticing, they found him a sort of exotic embodiment of liberty.

Franklin's look was so different to the normal formal powdered dandy thing they had going on at Versailles, that the French ladies found him rather attractive.

They would come up to him and stroke his furry hat.

Which he found amusing, but also he was quite pleased about, because he was winning them over to his cause.

But, underneath his furry old hat, Franklin was hiding a dark secret.