Sunday 4 May 2008 8:05pm - 10:05pm

A storm of hurricane-like proportions crashes into the coast, devastating the town of Wick in Scotland. It gets worse as a flood sets in and destroys everything in its path. The tidal reading is getting higher and a flood warning is put out as homes are destroyed and casualties increase.

Meanwhile in London everything is calm and the city shines in all its glory – its architecture, iconic river and the impressive edifice of the Thames Barrier gleaming in the sunlight.

Back in the sleepy village of Wick the flood is getting worse. It is all over the news showing shocking images of houses submerged and the death toll is increasing. Rob Morrison (Robert Carlyle) head of Atlantis Engineering is contacted by one of his staff who is in Wick where he is experiencing firsthand the extent of the damages as the storm continues.

It is a normal day at the Thames Barrier in London and Sam (Jesslyn Gilsig) is getting on with her day to day duties. She is fully aware of the storm in Wick and is keeping a close eye on the tidal gauges.

The Deputy Prime Minister (David Suchet) is being informed about the extent of the storm in Wick. His advisors are telling him the worst is over, but is it? He decides to visit the area to see first hand what destruction this storm has brought with it. He can not believe his eyes when he sees the casualties and it hits him how serious this really is.

Meanwhile Rob is called to the Thames Barrier for a maintenance check. His ex-wife Sam is the Barrier’s Director of Operations and she is the last person Rob wants to see. Meanwhile his estranged father, engineering genius Professor Leonard Morrison (Tom Courtenay) is desperately attempting to contact the Barriers command with a warning about the potential ineffectiveness of the structure. Upon receiving the news about his colleague drowning during the devastation at Wick, and with the soaring water levels and a unique set of weather conditions closing in, Rob realises that his father’s worst predictions are coming true. The reality is that the storm and the seasonal high tide will soon converge in the Thames causing a colossal surge, big enough to flood London.

Leonard explains to the Deputy Prime Minister that the Thames Barrier will not with stand the amount of water he predicts at high tide in three hours. The storm has changed its path and is heading south. One and half million people live or work around the flood danger zone so they must act quickly. After a dramatic forecast of the devastation to come from crisis control centre, COBRA, headed by Patricia Nash (Joanne Whalley) the Deputy Prime Minister begins the evacuation of the capital. Is it too late? They have not got long but Rob, Sam and Leonard must put aside their personal differences to mount an operation to save London from certain destruction.

There is panic on the streets of London and then the unthinkable happens: the Barrier is overwhelmed by an immense and terrifying surge. Water flows into London at a terrifying rate and volume, causing panic on the underground as the torrent cascades through the tunnels. Underground workers Zak (Tom Hardy) and Bill (Angus Barnett) are stuck in the tunnel with other commuters as the devastation continues as the city’s landmarks – Tower Bridge, the London Eye and Big Ben – are submerged.

Rob, Sam and Leonard are trapped at the barrier and Rob suggests they all jump for it to try and survive. Sam and Rob jump into the Thames but Leonard is too frightened to go through with it. He stays where he is as he loses sight of Rob and Sam. Leonard is rescued by a helicopter sent by the crisis control centre but he is concerned for his son’s safety.

The hospitals are chaotic and eight million Londoners are about to become heroes or victims as they struggle to survive the biggest disaster Britain’s capital has ever faced.