Starting with a very interesting idea about time (which I will not tell you for fear of spoiling the book, which is quite fun and you should read), Aldiss constructs a fun-to-read paranoid fantasy that fits it perfectly. The main character, Edward Bush, is one of the most skilled people alive at "minding", traveling into the distant past of our planet using a combination of drugs and mental techniques. As it turns out, traveling past is not so nearly as difficult, but the closer one gets to the present, the more difficult the goal. Bush can make it as close as 1920 or so, where he spends months watching a family of his direct ancestors live and die in a small coal town. Aldiss handles the paradox problem neatly. Minders cannot actually interact with the past, just watch helplessly, existing in a silent and spooky ghost-world without sound or smell. Creepy! Cool!