The general idea of the book was that a race of aliens in the form of trees travelled through space visiting other worlds and using their ability to send their minds into the brains of the creatures living in these worlds so that they could explore without being intrusive or being discovered.
They arrived on Earth and sent their minds into the animals they could sense and one found his mind in the body of a teenage boy in Glasgow, Scotland around the mid-to-late sixties.
Having found himself in the teenager, he discovered the primitive mind of humans had him trapped and unable to return to his tree body.
The story is a little comic and deals with the teenager finding his way in life and how he deals with things like his mother and girls while worrying the others on the ship would be coming for him as he was happy not to rejoin them.