' Just give a cup of water to one; and when you've helped one, move on to another.' Barbara Walker struggles under difficult conditions to keep alive the 67,000 refugees in Las Dureh camp, Northern Somalia. She is one of the vast army of missionaries who, at the season when families and loved-ones are reunited, endure separation from personal roots in their battle for a better world. Colin Morris , who went to Zambia 25 years ago, travels back to the mission fields of Africa on a journey that leads from a pioneer station in the Turkana desert to a London suburb, and gives a vision of how ' the call' will be answered in the future.