In 1913, a young, unschooled Indian clerk named Srinivasa Ramanujan wrote a letter to G. H. Hardy, begging that pre-eminent English mathematician's opinion on several ideas he had about numbers. Hardy, realizing the letter was the work of a genius, arranged for Ramanujan to come to England. Thus began one of the most remarkable collaborations ever chronicled. With a passion for rich and evocative detail, Robert Kanigel takes us from the temples and teeming slums of Madras to the courts and chapels of Cambridge University, where the devout Hindu Ramanujan, "the Prince of Intuition," tested his brilliant theories alongside the sophisticated and eccentric Hardy, "the Apostle of Proof." In time, Ramanujan's creative intensity took its toll: he died at the age of thirty-two, but left behind a magical and inspired legacy that today is still being plumbed for its secrets.