The opening episode of the second series follows events as St Mary's Hospital in Paddington receives victims from the Westminster terror attack on Wednesday 22 March. In the immediate aftermath of the terror attack on Westminster Bridge, three miles away a major incident is declared at St Mary's Hospital - the nearest of London's four major trauma centres.

"We are a hospital in the middle of London, we are a major trauma centre, we accept that the chances of there being a terrorist incident are higher for us to have to deal with than certain other hospitals," says the hospital's site director Lesley Powls.

Staff at the hospital have just minutes to implement the Trust's major incident protocol, including a gold, silver, bronze command chain, putting the hospital on lockdown and organising the transfer of some critically ill patients from the hospital's already full intensive care unit to sister hospital Charing Cross.

In A&E, specialist trauma teams are assembled, ready to receive the casualties as they start to arrive. Victims include students from a French school trip, 18-year-old Yann and 16-year-old Victor, and British victim Stephen, who needs immediate surgery to save his leg, and his wife Cara. "It's really hard when you spend so much time with somebody and then they're taken away from you and you're suddenly really, really alone. 'Cause you just want to grab hold of him, just give him a cuddle and a squeeze and take care of him but then he's so fragile, you can't, you just can't touch him."

In the days after the attack, staff at the hospital attempt to revert to business as usual and arrange for the repatriation of the foreign nationals caught up in the atrocity. Meanwhile the victims come to terms with what has happened to them. "There was a moment in the ambulance where I felt like I was going, I just wanted to sleep," reflects Yann. "I didn't know if I was going to die." "We're just an ordinary couple", says Stephen. "This will change us.".