Un détour par Diane follows the path of Diane, who desires men just as fervently as she despises them. When she finds out that her mother was raped in her youth, she is stunned. It's a surprise, but at the same time, it explains everything. Diane only has one goal in mind: to avenge her mother. Except that her mum has a different plan: to finally become the woman she should have been. With one woman wanting people to remember and another wanting people to forget, the whole situation becomes extremely tense.

Alex and Noémie, in their thirties, would like to have a child. But their plans are turned upside down when Alex's mother, Suzanne, starts doing crazy stuff. It's because she has contracted 'semantic dementia', a fatal neurodegenerative disease that affects her behavior. She spends lavishly, pays nightly visits to her neighbors to eat sandwiches, makes herself a fake driver's license with glue and scissors. Suzanne the mother goes to Suzanne the unmanageable-kid. A strange school of parenting for Noémie and Alex.