Shocked by the extent of corruption within its ranks, Scotland Yard set up a new anti-corruption unit in the early 1990s. Its members had to operate in conditions of unprecedented secrecy. They became known as the 'Ghost Squad'. Corrupt officers had access to the whole police computer system and anyone working undercover against them had to have a 'cover' that withstood scrutiny. Only now can the story of the 'Ghost Squad' be revealed. Award-winning BBC home affairs correspondent Graeme McLagan has followed the investigations since the beginning. He has interviewed undercover officers and many of the bent coppers they have exposed. This is the inside story of the 'Ghost Squad' and how it broke into the secret world of police corruption. Bent coppers really did believe they were untouchable: they stole cash and property, fitted-up innocent people and sold secret information to cripple court cases. Many of the bent coppers are now in jail or awaiting trial but the battle against corruption is not over. Graeme McLagan's gripping account reveals the ugly underside of London's police force and why teams from America and Australia have now come to Britain to find out how the Met is winning the battle against bent coppers.