Original: ISBN 0-385-51449-2 - Online excerpts: Opus Dei: An Introduction, Chapter I: A Quick Overview of Opus Dei, Chapter 7: Opus Dei and Secrecy Berglar, Peter (1994).
Simplified: ISBN 0-385-51449-2 - Some online excerpts are: Opus Dei: An Introduction, Chapter I: A Quick Overview, Chapter 4: Contemplatives in the Middle of the World, Chapter 7: Opus Dei and Secrecy Berglar, Peter (1994).