It follows how the elderly London thieves who were nicknamed "the bad grandpas" and the "Enfield Expendables" were recruited by an ex-con and carried out the crime. During a long weekend in April, the group tunneled into a London vault and carried the goods away. Most of the group now are serving time after pleading guilty to conspiracy to burgle with intent - except for one, who got away with $15M.
Essentially these guys were nabbed because they were analog criminals in a digital world; they were picked up by closed-circuit cameras and caught using their cell phones before and after the crime. Some six weeks after the burglary, the police raided the homes of the suspects.