Ronnie Biggs was a petty criminal who set out to transform his life with the daring heist of a mail train packed with money. The plan worked in ways he could never have imagined. Biggs was part of a gang of at least 12 men that robbed the Glasgow-to-London Royal Mail Train in the early hours of Aug. 8, 1963, switching its signals and tricking the driver into stopping in the darkness. The robbery netted 125 sacks of banknotes worth 2.6 million pounds — $7.3 million at the time, or more than $50 million today — and became known as...