
In The Ganymede Takeover the Earth has been taken over by giant intelligent worms from Ganymede who share a group mind. One of the rulers, called Mekkis, is given Tennessee to govern, which is considered a pretty terrible assignment. He has to deal with an internal war between the racists and a black power group. Mekkis cannot focus much on politics, however, because he becomes so obsessed with the topic of human psychiatry that he eventually causes the whole Ganymedan race to self-destruct by infecting its group mind with his visions of an existential hell.
There is also a telepathic radical, Percy X, who is leading a revolution but becomes so unbalanced that he almost destroys the world with a "hell weapon." This is an apocalyptic scenario that the human race ends up narrowly avoiding in the end. It's a real 60s novel; one could imagine a version directed by Stanley Kubrick, with maybe Godfrey Cambridge as Percy X?
This book was a collaboration with Ray Nelson, who was also a cartoonist and inventor of the propeller beanie. Again, it does not represent Dick's best work when considered in isolation, but if you're reading the other PKD novels of the 60s, which are extremely addictive, by all means add it to your list. These books sometimes tend more towards the sociopolitical, as in the case of The Penultimate Truth, The Game Players of Titan, and this one, while others like Ubik are more ontological, or gnostic like A Maze of Death, or concerned with the relationship of empathy to human consciousness as in Do Androids Dream of Electric Sheep? To me, this meganovel ( consisting of 22 novels in all) is Dick's greatest work, and one of the landmarks of twentieth century literature.