Eric Vincent is in his thirties and lives an uneventful life with his wife Audrey. They are talking about having a child. Eric is contacted by a friend of his biological father he never knew about the latter's death. Eric can come and collect his father's ashes. He is reluctant but then accepts.
The Key closes the dark and complex detective trilogy of William Nicloux. We find in this film, in supporting roles populating the parallel plots that Eric Vincent (Guillaume Canet), the characters of François Maneri (Thierry Lhermitte), the investigator of a private matter, Une affaire privée, and Michèle Varin (Josiane Balasko), the police captain in That Woman, the second part.
