A 17-year-old tourist stabbed to death. A young woman taken hostage and raped. Just two of the 16,000 crimes that occurred last year on London's Underground. For the first time, a BBC film crew goes undercover with the 'Moles', a specialist. Underground police unit. Heavily outnumbered, the 'Moles' contend with an army of muggers, pickpockets, molesters, drunks and hooligans. As for the Guardian Angels: 'They've got to be a good idea,' says one detective.
