Living underground for 40 days without any notion of time: this is the challenge launched by explorer Christian Clot to 7 men and 7 women, a world first. How to adapt to this extreme confinement? How will the group interact in these unique living conditions? How will the body and brain respond to the loss of temporal reference points? Immersed in one of the largest caves in Europe with these timeonauts, this film tells the story of an unprecedented collective human and scientific experience.