This is another outstanding book in Piper's biography series, The Swans are not Silent. This volume of 155 pages covers the lives of Augustine, Luther and Calvin. Though available as free audio downloads from Desiring God, there is something about having the words in front of you to ponder and reread. The introduction alone on learning from flawed saints is worth the £8.99. If you want to learn about these three great men of the faith and how to read biographies and distill them then this series by John Piper is a must.