Louna sets off with Charlotte and Éloi on an expedition to find a cure. Can they really trust her? Sammy, meanwhile, works on the equations with the pyramid's data and makes a game-changing discovery.

The kidnappers demand a ransom to free Charlotte and Éloi. Zoé, overwhelmed by the situation, hesitates, while Mathilde and Billi act behind her back. Florence sinks into despair when she learns that the miracle plant doesn't exist.