Stone by Adam Roberts deals with a criminal in a future utopia.
When we first meet our protagonist being held in a prison in the centre of a star, and has just been sentenced to execution by having the nano machines in our protagonist's blood removed. (The nano machines keep citizens from harm and allow them to lead very long lives.) Before long the main character, Ae, is contacted by a mysterious stranger who promises to break Ae free in return for doing a small favour. The favour is that Ae must wipe out the population of a planet without harming the planet itself.
This short book (under 300 pages) is a very good and interesting read. Roberts is an author who likes using Science Fiction to explore ideas and this book is no different. The fact that it is short means it flies along without much padding and this helps the story to move along.
Well worth reading.