Knights of the Black and White, by Jack Whyte
Knights of the Black and White (©2006)

Templar Trilogy, Book 1
by Jack Whyte

A Brother of the Order—a medieval secret society uniting noble families in a sacred bond—Sir Hugh de Payens has emerged from the slaughter of the First Crusade a broken man seeking to dedictate his life to atonement, and to God. But the Order has other plans for the knight and his brethren. They must embark on a search for the Order's hidden treasure and the true roots of the society, protected for thousands of years in a location deep within the Temple Mount of Jerusalem. It's an insane task, for which de Payens has devised a dangerous plan—one that could not only expose the Order's riches but also reveal a secret that could shatter the very might of the Church itself.