ATTENTION: Do not read this unless you are willing to be spoiled!
By the end of Collateral, Ashley is spending a lot of time with her Extremely Enlightened Professor, Jonah who is perfect (much like Cole was at the beginning of the novel... ahem) and it looks like she's going to start a relationship with him. The pair come across Cole waiting at Ashley's apartment after they've had dinner and Cole breaks Ashley's jaw and Jonah's ribs. Ashley calls off her wedding and at the end of the novel it appears that she's poised to be with Jonah. I was saddened that by turning Cole into a monster, Ashley was relieved of having to make a choice. It gave her permission to move on without her having to ever be the bad guy. Instead, Cole bore that burden. I would have loved the ending to be more risky, perhaps with Ashley leaving Cole, not for another (and more enlightened, naturally) guy, but for herself. In the end, I felt like Ashley was never forced to grow as a character as a result of the author's choices about the conclusion to her story.