The ending!???!

At first, aside from the obligatory F-Bombs and the change of setting, this movie was on track with the book; however, the ending of the movie sent me reeling! I wonder how Lois Duncan feels about her work being mangled by Hollywood execs? Why base a movie on a novel and completely change the most important part--the ending! It was bad enough when Glenn became the hero in the end, but why make Marianne's step-dad a part of the conspiracy? To me, this ruined what Duncan intended--for Marianne and her stepfather to finally connect and work together instead of against each other. I was very disappointed, to say the least!