Dion Fortune 
Psychic Self Defense (annotated) 

It is with a sense of the seriousness of the issues involved that I set myself to the task of writing a book on psychic attack and the best methods of defence against it. The undertaking is beset with pitfalls. It is hardly possible to give practical information on the methods of psychic defence without at the same time giving practical information on the methods of psychic attack. It is not without reason that initiates have always guarded their secret science behind closed doors. To disclose sufficient to be adequate without disclosing sufficient to be dangerous is my problem. But as so much has already been made known concerning the esoteric teachings, and as the circle of students of the occult is becoming rapidly wider every day, it may well be that the time has now come for plain speaking. The task is not of my seeking, but as it has come into my hands, I will do my best to discharge it honourably, making available the knowledge which has come to me in the course of many years’ experience of the strange by-ways of the mind which the mystic shares with the lunatic. This knowledge has not been attained without cost, nor, I suspect, will the divulging of it be altogether free from cost, either.