The life of Etienne-Jules Marey, the 19th century pioneer of photography and cinema, famous for studying animal and human locomotion.

Having lost her job, Beatrice accepts from a friend, an unhappy businesswoman, an indelicate little job: to put a certain Paule Caret, who is said to be a drug dealer, on the phone. Seduced by the voice of the latter's lover, Beatrice tries to meet him...