The man who stole the atomic bomb. And why he did it. 

Klaus Fuchs was a talented scientist - but he was also a Soviet spy. He worked on the British American atomic bomb project, whilst handing nuclear secrets to the Russians. Host Rosa Ellis uncovers the double lives of Klaus Fuchs and her great-aunt Ursula.

The world’s most dangerous spy? 

A young scientist’s journey into espionage. From a German pacifist family to a Soviet spy ring. Physicist Klaus Fuchs flees Nazi rule for England and joins the race to develop an atomic bomb – whoever gets there first wins the war. Presenter Rosa Ellis discovers how Fuchs’ double life begins. 

The fate of the world is decided: Klaus Fuchs joins a top-secret atomic mission. The race to build the bomb is on. In Birmingham, England, Klaus Fuchs is working on “TUBE ALLOYS” – the codename for the British atomic bomb project. But at the same time, he’s slipping secrets to the Soviets. Host Rosa Ellis finds out how he did it. 

The spy meets his spymaster - presenter Rosa Ellis' great-aunt Ursula. She's a housewife and mother living in the English countryside. And she also works for the Soviets. Fuchs and Ursula have a secret list of information that Russia urgently needs to win the nuclear race. Together, they could be the most dangerous spies on the planet. 

A double life gets more dangerous. Fuchs joins America's bomb project and the race with Russia is on. But as the nuclear mission ramps up, security tightens too. Now at the heart of the mission, his skills in science and espionage are tested to the limit

Lives are on the line. The Fuchs family is drawn into the espionage as the atomic bomb project takes a deadly turn. Klaus is at the covert Manhattan Project laboratory in Los Alamos, New Mexico. In this desert terrain, he has lost contact with the Soviets. As the countdown to detonation begins, there's only one person who can be trusted. 

The interrogation of a spymaster. Ursula is questioned as Klaus Fuchs returns to England. Secrets threaten to be spilled and loyalties are tested. The war has ended, and the physicist could have a promising future. But will his past catch up with him? Could British intelligence services be on to him? 

The spy catchers close in. Klaus Fuchs is caught in the crosshairs. Spymaster Ursula has outwitted the interrogators - but can he? As he settles down in England, British intelligence services are following him at every turn. He is caught in a web of surveillance - and his faith in the Soviets is faltering. How long can he run for? 

A double life implodes. Klaus Fuchs faces judge and jury, but will he confess? A future as an eminent physicist is slipping away. And the friends who took him in as a young scientist are blindsided - they want answers. But first he must face the court. 

Jail awaits - Klaus Fuchs is going down. But will he take his spy handler Ursula with him? British intelligence wants names. As Fuchs is forced to face his past, Ursula tries to run from hers. Series host Rosa Ellis questions how their actions have shaped today's nuclear tensions.