Steal across the sky by Nancy Kress (Tor, 2009)
This science fiction story has a unique premise which I won’t reveal. You should read it for yourself. I will say that 21 humans are selected by an alien race to visit several planets and “witness” a situation that they are expected to bring back news about to the Earth. The book takes place in a near future (nearer now than it was in 2009) early 2020’s that is not much different from the present. It tells the story of several young people who are selected for space travel, interact with the people on the other planets, and come back changed. In fact more than half of the story is what happens when they come back. This is the sort of book you will have to read to the end before you can go to sleep.