Three friends are preparing for a gruelling dash across eastern Europe which will see them run 39 marathons in 33 days as part of the fight to end child trafficking.
Tom Stancliffe, Guy Hacking and Rob Martineau will pound the roads from Odessa in the Ukraine to Dubrovnik in Croatia, covering more than 1,000 miles on a journey through nine countries.
The trio will run up to 60 miles per day, carrying their supplies on their backs, and will spend most nights sleeping rough in villages.
The challenge will take them over some of eastern Europe's most remote terrain without the assistance of support vehicles or medical aid.
The three Londoners will endure freezing nights in the Ukraine, snow storms in the mountains of Montenegro and face the threat of wild dogs in Bosnia. During the journey, they will pass through countries known for people-trafficking, including Moldova, Romania, Bulgaria, Macedonia, Kosovo - where they will complete their longest stretch of more than two marathons in one day - and Montenegro.
Mr Stancliffe, a lawyer at Allen and Overy who has run the famously tough Marathon des Sables across the Sahara Desert in Morocco, admitted he was "terrified" at the prospect of arriving in Odessa with nothing but a backpack.
"The hardest thing will be trying to ensure your body withstands the trauma of running well over a marathon each day and recovers itself to cope with the challenges of doing the same thing the next day (for 33 days)," he said.
The 29-year-old, from Pimlico in central London, added: "Hearing stories about trafficking emerge in the media last year made me realise that human-trafficking is happening on a shocking scale in the UK and across Europe and it is tragic to think of the devastating impact it has on children's lives. I think standing up to such a fundamental injustice is important and we wanted to rally people together to do something to help."
Mr Hacking, 30, an investment and asset manager from Brixton, south London, said the most concerning element was "the unknown". He said: "We don't know if the route is the best one. We don't know how cold it will be or where we will sleep each night. We just don't know if or when we will pick up an injury or how to treat it."
During their run, they will stop to meet charities and politicians in the cities of Bucharest in Romania, Sofia in Bulgaria and Pristina in Kosovo. The group aim to raise £150,000 to enable trafficking charity Love146 to build the UK's first residential trauma recovery centre for children.