This article presents the history of one until now unknown case of C.G. Jung: Maggy Reichstein. Born in Indonesia in 1894 in a very aristocratic family, she brought her sister to Zurich to be treated by Jung in 1919, and later she herself was in analysis with him. Jung used her case as example in his lecture in 1937 on the realities of practical psychotherapy, relating it to the process of transference and countertransference. Jung deepened his studies in Eastern psychology after a series of dreams she had, which culminated in the Yoga Kundalini Seminars. She was also the case presented in his article of 1951 on the concept of synchronicity. Jung wrote that her case, concerning synchronicity, remained unique in his experience. Jung also published some of her mandalas. He considered her able to understand his ideas in depth. Reichstein was for Jung an important case, which challenged and triggered his interests in different subjects.