Elsa, an eight-year-old girl, and her mother, a young woman named Isabelle, have just moved into his apartment building.

Julien gives her shelter one afternoon and explains butterfiles to her but he bars her after she goes into a room he has told her is out of bounds and lets some escape.

Julien decides to go to the Vercors plateau for a week in search of a rare butterfly, Isabelle, which lives for only three days.

During their search, Julien reveals that his terminally ill son had asked him to find the Isabelle butterfly which is why it was so important to him.

Elsa ends up falling into a deep hole one night and Julien asks the authorities for help.