Caldwell travelled widely in the USA and Europe visiting and studying results in the practices or clinics of psychiatrists using LSD as a psychotherapeutic tool. In the book he gives an excellent synthesis of the mass of information and experience gathered.
I come back to this book again and again because Caldwell has given such a wide map of the worlds of experience one meets during any prolonged inward exploration or therpay. What he says does not simply apply to LSD, but to any real personal growth. However, this is the real stuff, not just the fantasy hopes of achievement. Therefore it includes not only the experience of samahdi/enlightenment or oneness, but also the inner traumatised child, the meeting with the betrayal we may have felt as an infant, and the murder we would like to commit on those who hurt us.