This is the extraordinary story of the famous psychoanalyst Carl Jung and the groundbreaking physicist Wolfgang Pauli's struggle to quantify the unconscious. Pauli was fascinated by the inner reaches of his psyche and not afraid to dabble in the occult, while Jung looked to science for answers to the psychological questions that tormented him. In 1932, they met. Their friendship led them, in Jung's words, into 'the no-man's land between physics and the psychology of the unconscious...the most fascinating yet the darkest hunting ground of our times.' Both were obsessed with the far-reaching significance of the number '137'. Their quest to solve its enigma led them on a lifelong journey into the secrets of alchemy, the work of Johannes Kepler and the "Chinese Book of Changes". This is the story of the remarkable and fruitful collaboration between two of the greatest thinkers of the twentieth century.