The book describes how each leader came to power, and how Saladin managed to gain enough support in the Muslim world to put together an army and recapture Jerusalem. The Christian response was the Third Crusade, a massive undertaking lead by Richard I of England. We hear how Richard was the more inspiring leader, being often in the thick of a battle, where he seemed virtually invincible - it is fascinating to see how one man could make such a difference. He managed to recapture the coastal cities, but it eventually became clear that even if Jerusalem could be captured, it couldn't be held - too many of the crusaders were eager to return home.
The book is fairly limited in scope - there isn't much about the other crusades, or non-military life at the time. I didn't see this as a problem though, as it is well written, and so inspires the reader to find out more about this period of history.