I'm Emily Strosser.

My grandfather worked on the first atomic bomb, and in 2020, I investigated another man

who helped to build the weapon that would change the world.

Leo Zalard, the scientist who might have stopped it.

But the story didn't end there.

Coming soon, the next chapter.

In the meantime, I'll be taking you behind the scenes to meet the team as they unravel

the mystery of the man who stole the bomb.

We really wanted to know why they did the things they did, but also about the impact on

the people around them.

They were both so committed to their ideology, but they were keeping secrets from the people

they loved.

Here's the presenter of Season 2.

Analyst Rosa Ellis, who's great aunt, has a key connection to this story.

Series 2 of the bomb is all about a man called Klaus Fuchs, who was a nuclear scientist,

but he was also a spy for the Soviet Union.

And who is Ursula Kaczynski, a.k.a. agent Sonja?

Ursula Kaczynski was my great aunt.

She was not just a spy, she was a spy master, she was a colonel in the Red Army, and she ran

spirings in China, Poland, Switzerland, and England.

And probably the most important spy she worked with was Klaus Fuchs.

She grew up in Berlin during the rise of fascism, and she was Jewish, so it was a difficult

...