Season Four opens as a harsh truth lands on the shoulders of those who remain: Earth's nuclear reactors are melting and will soon set the atmosphere ablaze. Is anything left for our heroes to fight for? Can they find hope knowing the end is inevitable? Will they spend their days trying to survive? Or use their limited time to finally live? The stakes have never been higher. Alliances are shattering and fragile societies are on the brink

Ninety-seven years after nuclear Armageddon destroyed our planet, humanity's sole survivors live on the Ark, an aging space station experiencing overpopulation and inadequate resources. When faced with difficult choices, the Ark leaders chief medical officer Abby, Chancellor Jaha and the mysterious Kane decide to send 100 juvenile prisoners back to Earth to test its living conditions. Among them are Clarke, Abby's bright daughter; Wells

Set almost 100 years after mankind nearly destroyed itself in a nuclear Armageddon, the surviving human race aboard the orbiting “Ark” space station take the first step to recolonize Earth, by sending 100 juvenile delinquents back to the planet’s surface to see if it is habitable. In the first season, they discovered that the Earth is not quite what they imagined – and that they were not alone.