Dreamfall is the third book in Joan D. Vinge's Cat series. Please read no further if you have not read this book and you don't wish to be exposed to mild spoilers.
Dreamfall has Cat on a strange planet with a research team, and it is the least enjoyable in my opinion, which makes it about six times better than all books anyway. Dreamfall is the story of Cat's exploration of his heritage. While traveling to a distant planet with his university to study the "cloud whales," Cat goes to the "Homeland" (where the indigenous Hydran population lives, much like Native Americans were pushed off of their land to reservations) and ends up in a mess. His telepathic talent still doesn't work except maybe once in a while, so he finds he isn't really welcome over in the Hydran town because keeping his mind closed is offensive to them. As he is feeling hopeless about not fitting in with either the humans or the Hydrans, a woman smacks into him, running away from security, and drops a child's databand into his hand as she runs away. He helps her escape and ends up taken into custody himself.
He is interrogated and briefly tortured, but since he knows nothing he is unable to help them catch the Hydran woman, who apparently kidnapped a human child. It comes out that the child is Joby, a baby with neurological damage that makes him unable to control himself at all, and so his family hired a Hydran companion for him to make him able to move and react the way he wanted to and try to rehabilitate him. The woman, Miya, took off with their son for reasons unclear. Cat feels a connection to the woman, though, and ends up meeting her again very soon, when she explains herself to him. She takes him to the Hydran town and tries to help him get to know the people, though her sister, Naoh, takes an immediate aversion to him. Miya and Cat become lovers, and Cat learns the Hydran language and attempts to act as a go-between for the humans and the Hydrans. But trouble is brewing (of course). The humans see the Hydrans as terrorists holding the child hostage, and the Hydrans--specifically a freedom-fighting radical group of them--see the humans as invaders. They are led by Naoh in a fight against the humans, and Cat is swept up in it, yet again, trying to find his feet. Cat thinks Naoh is wrong and very sick, and tries to stop the Hydrans from attacking the humans, but Naoh is too persuasive and ends up getting hundreds of people to riot. And the humans retaliate with a kind of gas that makes Hydrans unable to use their psionic abilities, rendering them helpless and confused. Cat, Miya, and Joby retreat to a quiet place to heal.
There are tons of details I've missed here, of course--Cat's attempts to expose Corporate Security's treatment of their bonded workers; Cat's friendship and relationship with Kissindre Perrymeade, his classmate who is somewhat entranced by him; his relationship with an old woman known as an oyasin who teaches him much about life and himself. But of course it all comes together in an ending that definitely isn't "happy" but just seems right. Cat is much more mature now and his exploration of the Hydran part of himself is fascinating; he always felt very human because of being raised thinking he was only human, and so it's great to see his acceptance of both halves.
Other books by Joan D. Vinge: Psion and Catspaw