A year after the lost battle against the experiment, Kate Jones is once again targeted by the organisation and a revengeful Jack Smith and Helen Day. After the apparent loss of Jack, her brother Charlie and dozens of others, it is now up to Kate to discover the truth and protect the world from the approaching threat. With a global telephone call aimed to have catastrophic effects on every single human being who answers, the race is on to prevent the organisation from releasing the '555 Drug' worldwide. Who will survive as the series reaches its heroic finale.