The book "The True History of the Sin of Man" by Mukundan P.R. tries to bring to light the revelations of Navajyoti Sri Karunakara Guru, the Founder of Santhigiri Ashram at Thiruvananthapuram in Kerala, India. The most important revelations of the Guru that looked almost like a riddle to me are Guru's concept of "Manu" and the original "Sin of Man" which is a little different from the popular myths. The original sin happened many ages ago through Satyatrana, a great spiritual master, reveals Navajyoti Sri Karunakara Guru. The sage Satyatrana was a powerful spiritual authority in a pre-historical age. Once, he was in a state of deep spiritual absorption. In his great spiritual ecstasy, he uttered 'I am God'. He mistook himself as the Supreme instead of thinking he was only God's creation. This was the First Sin of man, which distanced man from God. The revelation of Navajyoti Sri Karunakara Guru about the original sin of mankind is very significant because it explains why man is living in forgetfulness of God's Will from time immemorial. Similar is the Guru's revelation about spiritual stages and the deviation that occurred in Sanatana Dharma, the Eternal Spiritual Order many ages ago. The book deals with a wide range of questions related to cosmogenesis, spiritual evolution, the secrets related to the planetary system, the astral biospheres a soul must pass through before God-realization, as well as the dangers truth seekers encounter in the path.