Monday 5 May 2008 9:00pm - 11:00pm

This is turning out to be the worst natural disaster Britain has faced as the extent of what has happened unravels. The Deputy Prime Minister (David Suchet) is frantic as the situation continues to worsen.

There are people everywhere trying to survive the deep flood waters, but will their efforts be in vain? Professor Leonard Morrison (Tom Courtenay) is back at the COBRA crisis control centre, and he is their last chance of hope. They need his help desperately but his mind is elsewhere thinking of his son and daughter-in-law - are they alive or dead?

Unknown to Leonard Rob (Robert Carlyle) and Sam Morrison (Jesslyn Gilsig) are still fighting for their lives. They discover survivors on their route to survival which gives them hope for the rest of the city.

Professor Morrison is still sure that everybody is still at high risk unless they do something quick. He starts making his calculations as he knows his son is still out there somewhere. He gets the phone call he has been waiting for as Rob and Sam have narrowly escaped the Barrier with their lives. Between them they have decided there is only one way to save the city from total devastation; they must return to the submerged control room on the barrier and implement a high-risk plan to drain the city of water.

Thousands of people have been reported stranded in the city and the emergency services have been stretched to their limits trying to evacuate everyone at risk. The view of the city is one of total carnage as bodies float in the waters and survivors look few and far between with no food, water or warmth.

The team only have one chance, it’s a race against time and the lives of millions of Londoners are in their hands. Sam, Rob and Leonard are re-united to save London but who will go to the barrier and sacrifice their own life and will it be enough to save the city?