The main criminals are a group of South-East London gangsters, including Lee Wenham, who comes from a notorious Gypsy family and was destined for a life of crime. Their motivation is to pull off one of the most audacious heists by stealing a rare diamond collection worth £350 million from the Millennium Dome in broad daylight, aiming for a high-stakes, high-reward crime.

The criminals planned to ram-raid the Millennium Dome using a bulldozer or truck, grab the rare diamonds including the 203-carat Millennium Star, and escape by speedboat down the River Thames. Their plan was elaborate and felt like a scene from a James Bond or Mission: Impossible movie, involving a bold daylight attack and a fast river escape.

The Metropolitan Police's Flying Squad had been surveilling the criminals closely and were prepared to stop the heist. They tracked the gang's movements and ultimately caught them in the act, preventing the theft from succeeding.

The series includes real interviews with both the criminals involved and the police officers who handled the case, providing perspectives from both sides. This approach gives the story an authentic feel and allows viewers to understand the events from multiple viewpoints.

The diamond at the center of the heist is the Millennium Star, a 203.04-carat, D-flawless, pear-shaped diamond owned by De Beers. It is considered one of the world's most valuable gems and was the centerpiece of the Millennium Jewels collection exhibited inside the Millennium Dome.