John Wesley is a fiery preacher who is stirring up the people on the streets of London. One day, while peddling his father's wares, young Robert Upton meets Wesley and his life is changed forever. Robert and his father start going to Wesley's meetings whenever they can. Gradually, Robert begins to understand what Wesley's preaching is all about. As he allows God to work in his life, Robert finds that his own heart, like Wesley's, is strangely warmed.