When William Booth met Catherine Mumford in 1852, it was the start of a story that would change the lives of millions of people across the world. Out of their love sprang a new and radical international Christian movement ‘ The Salvation Army. Throughout their life William and Catherine, when apart, exchanged letters and notes expressing not only their deep love but also a lasting friendship and mutual respect which would survive the challenges of separation, ill health, the struggle of raising a large family, opposition, disappointment and professional uncertainty. The letters, spanning nearly 40 years, reveal both the everyday minutiae of life in Victorian times, and the challenges of being revolutionary Christian thinkers in the second half of the 19th century.