It made a great impression on me at the time. It was probably a few years old when I read it, if I remember the condition of the binding correctly. The scene/s that stick in my mind have the protagonists, who are in some sort of resistance movement, hiding out, and they need to keep on guard because the enemy comes at them by telepathy, but they fight back likewise. I picture one such scene actually taking place in a cellar, with the camaraderie of the good fight and a home-front touch a fifteen year old could delight in. There were rather well-drawn-out rules for how the good guys and the bad guys could operate telepathically, so the reader could tell the good from the bad as a morality theme, and it was not an impossible struggle, either. Thanks.
A lone ship of the Stellar Patrol crash-lands on an out-of-the-way planet. Quickly scouting around, the crew find evidence of a long vanished hi-tech civilization in the Sealed Cities, along with nomadic hunter-gatherer level groups of humans. When the rangers enter one of the cities, they find it occupied by another group of refugees and ruled by the Acturian Cummi. A master telepath, bent on becoming the planet's sole ruler, Cummi is not above controlling other people's minds. Zinga, a member of the Zacathan race, along with the human Kartr, both higher-order telepaths themselves, end up in a fierce mental battle with Cummi. ~ Edited from Amazon.com
Note: You can read the book in its entirety here :-)