"It was Christmas Eve and I was in charge of decorating the dining table,” said Lizzie with her typical sunny smile, "when we got a call asking us to fly into Gereida to treat nine wounded civilians. As usual, it took us ten minutes to get ready, a few hours to gather the necessary paperwork and official permits, and 25 minutes to fly from Nyala to Gereida.”

Lizzie is one of two nurses on the ICRC's Field Surgical Team (FST), a group of four medical staff based in the southern Darfur city of Nyala. Their job is to fly around Sudan and operate on people wounded by fighting.

"We can operate anywhere,” says Lizzie, “as long as we can hang a mosquito net. And if we have to, we can just hang a mosquito net between our two trucks." Those of us brought up on TV programmes full of high-tech operating theatres will have trouble imagining a surgeon working under a baobab tree, but that is the usual setting for most of the FST’s operations.

The surgeon, anaesthetist and two nurses set out across the country with minimal equipment, often working long hours to treat people unable or unwilling to go to hospitals or clinics. Some are too far from the nearest hospital, others are scared of being spotted by the other side. Whatever the reasons, they call the ICRC for help. "All they need to do,” explains Dr Tesfayeh in his deep voice, “is get in touch with the ICRC."

Dr Tesfayeh is from Ethiopia. He is a veteran war surgeon who has spent many years performing complex war surgery in his own country and around the world. He tells me about his daughters and his life back home, punctuated by emergency missions in Afghanistan, Sierra Leone, Cambodia and elsewhere.

All the members of the Field Surgical Team are medical professionals with lives in their own countries, but they undertake ICRC assignments in war-torn areas for several months every year. I asked Lizzie how it felt to move from Copenhagen to a field operating theatre in Darfur. "Surreal,” she answers, with a faraway look. "The most difficult experience was my first mission in Beirut in 1982. Working on a boat with traumatized war casualties in the middle of a Mediterranean storm felt like doomsday. The images of those people haunted me for weeks after I returned to Denmark. The whole world looked different." She has worked in many other disaster areas since then: the Pakistani-Afghan borders in 1985, Jerusalem during the Intifada, Indonesia after the Tsunami in 2005 and Kashmir in the aftermath of the 2005 earthquake.

The Field Surgical Team started in 2005. They have their own aeroplane, which can carry almost half a tonne of medical and surgical equipment, but before the team deploys it must be sure that it will be welcome: any armed group that controls the route or the final destination must guarantee their safety. It usually takes a day to secure these guarantees, after an intense series of phone calls. The team then boards the aircraft and heads to the nearest city where the ICRC has an office. From there, they get into two ICRC trucks and drive to where their patients are waiting.

Another condition of deployment is that there must be at least three patients with life-threatening injuries such as open fractures resulting from bullet wounds to the limbs, or bullet wounds to the head, abdomen or chest. "Of course, we deal with other injuries while we’re there. On our last deployment, we treated a small boy who had broken his wrist falling out of a tree,” said the head surgeon.

The missions that take members of the Field Surgical Team around the world are on a level quite separate from life at home. They compare it to moving from a colour film to black and white. An opportunity to step out of one life and into another, alternate rhythms and paces and gain a richer perspective of the world around them. Even as they talk to me in their office at Nyala, Lizzie and Dr Tesfayeh await the call that will take them on their next adventure.