S1, E1: Timely yet terrifying, Flood predicts the unthinkable. When a raging storm coincides with high tide it unleashes a colossal surge, which travels mercilessly down England’s East Coast and into the River Thames. Overwhelming the Barrier, torrents of water pour into the city. The lives of millions of Londoners are at stake. Top marine engineers and barrier experts Rob, his ex-wife Sam and his father Leonard Morrison, have less than two hours to save the city from total devastation.