Author and filmmaker Jon Ronson asks, how do agnostics come to Christianity?
Increasingly, it's through Alpha, a course devised many years ago in a well-heeled church in London's Knightsbridge, but which now operates in tens of thousands of churches of all denominations, in universities, prisons and military bases across the world.
Over 11 million people worldwide have now attended an Alpha course. But what happens on it? And do agnostics really become Christians in such a short space of time?
Afforded complete access to one Alpha course, at St Aldate's Church in Oxford, Jon documents the whole process over its eight weeks.