The film depicts a devastating flood which strikes London when the Thames Barrier is overwhelmed by a huge surge of water.
Rob Morrison (Carlyle), the head of Defiant Engineering, is called to the Thames Barrier for a maintenance check. There he meets his ex-wife Sam (Gilsig), the Barrier's Director of Operations. Meanwhile Rob's estranged father Leonard (Courtenay), a professor in meteorology, discovers that a storm which had struck Scotland and originally thought to be heading for Holland has now diverted back towards South East England and London. He predicts that the Thames Barrier will not be able to hold the back the immense pressure if the storm surge hits at high tide.
With this information at hand, Rob, Sam and Leonard warn COBRA Supervisor and Met Police Commissioner Patricia Nash (Joanne Whalley) and Deputy Prime Minister Campbell (Suchet) of the imminent danger. However, with only three hours until the surge hits, it may be too late to save the city of London.
