Wright examines the techniques of intelligence services, exposes their ethics, notably their "eleventh commandment", "Thou shalt not get caught." He described many MI5 electronic technologies (some of which he developed), for instance, allowing clever spying into rooms, and identifying the frequency to which a superhet receiver is tuned. In the afterword, he said that he wrote the book chiefly to work to regain compensation for losses of significant pension income when the British government ruled his pension for earlier work in GCHQ was not transferable.