Early on Christmas morning in 1962, the Indian diplomat S.S. Banerjee heard a mysterious knock on his door in Dacca, East Pakistan. Standing outside in the darkness was a 14-year-old boy, who beckoned to him to follow, and minutes later Banerjee found himself opposite the firebrand politician Mujibur Rahman, a pipe-smoking Bengali activist who had recently transformed from a Pakistani nationalist into one of the country’s fiercest critics.