10pm on a summer's evening. The sun goes down over the Place de la République in Paris. Lucie and Rio embark on an "urbex", descending into the city's abandoned underground networks. The two teens share their adventure live on social media. On a subway platform, two young lawyers are on their way to join some friends. They film themselves as they wait for the train. Nora and Djibril have just made love. While he heads off to work, she meets a friend for the evening. None of them yet know it, but moments later, a terrorist attack will change their lives, linking their destinies forever. In a few moments, they are about to enter the darkness. The fiction unfolds through three simultaneous video feeds, filmed on cellphones and available to all via social media.