Shin has long been one of the most popular forms of Buddhism in Japan. As a devotional tradition that emphasizes gratitude and trust in Amida Buddha, it is thought to have little to do with secrecy. Yet for centuries, Shin Buddhists met on secluded mountains, in homes, and in the backrooms of stores to teach their hidden doctrines and hold clandestine rites. Among their adherents was D. T. Suzuki's mother, who took her son to covert Shin meetings...