"What you need to kill someone?" - "A good reason"

Marianne is twenty, she was sentenced to life imprisonment for triple murder. Violent and uncontrollable, she saw hell in prison. But one day, three policemen come to visit him; they have a market to offer him kill to regain his freedom ...
This novel devours thousand pages in one go (in any case that's what I did ^^). Karine Giebel has a style all its own, very fluid. However, I found the first part of which takes place in prison is too long: a lot of repetitions and hackneyed situations and a love story a bit too "rose water" to me.
However, I admit that the second and third parts of the novel are panting (I can not say anything more on pain spoiler, sorry).
As for the characters (the nicer the most infamous), they are very well drawn; Giebel really ensures level psychology.
Finally, I recommend this book to fans of suspense and good detective stories, a bit like Nikita ...