The relation between Patrick and Karine seems be, more than the crime attempt against renan, the basic axis of film. Divorced, united by their son, both preserving noble feelings for the other but being not so close to define them in proper manner, their story represents the source of interests.
Sure, in a film where a theater play, templars, castles, an eccentric director are present, near the curiosity of a boy and his first romance, it is difficult - and unfair - to not be seduced.
The answer to murder, more precise, its motivation, is , in same , measure, a precious good point.
In short, familiar recipe, interesting development of it.