Sarah's Key is one third of an incredible film. New comer Melusine Mayance has a star making performance as Sarah during her youth. On her first performance in a feature length film (not including her performance in the 2009 Italian film Ricky, which despite technically a feature length film, was never distributed to more than one theater, and grossed less than $2,000), she pulls off the feat of making the audience desire her to be in every scene rather than veteran actor Kristin Scott Thomas.
The reason why I had said "one third" in the previous paragraph, was because nearly every aspect of the "holocaust" story worked incredibly well. Natasha Mashkevich and Arben Bajraktaraj are both phenomenal in their supporting roles as Sarah's parents, and Jonathan Kerr also does a great job as the concentration camp worker who allows Sarah and her friend (also played very well by another newcomer Sarah Ber) escape from the camp.
Nearly all of my problems with the film came from the second plot that takes place in the modern day. Actors James Gerard and Karina Hin join the ranks of Ken Jeong in The Hangover and Jessica Barden in Hanna playing Kristin Scott Thomas' assistant and daughter respectively. Despite the two of them having (very) supporting roles, every line that comes out of their mouths in this film completely took me out of the story.
Another problem Sarah's Key faces is the lack of any type of dramatic suspense in the story set in the present day. As an example, when Kristin Scott Thomas interviews a member of Sarah's family, she is told that Sarah was killed in a horrible car accident. Unfortunately, director Gilles Paquet-Brenner shows this accident, and because it's so clear that Sarah drove into the truck that supposedly crashed into her, what is supposed to be the climax of the film (that Sarah committed suicide) fails.
Despite having one third of a great film, Sarah's Key is undone by a melodramatic and poorly acted second plot which unfortunately takes up most of the film. If the entire second plot was excised, and the film was released as a short, the grade would probably be an A-. However, it wasn't.