This is the fourth in the Crowner John series, and while 'The Awful Secret' is a good read, its claim to rock Christendom to the roots never quite gets there.
The plot revolves around two rogue Templar knights who discover in the Temple vaults in Jerusalem, 'the awful secret', that causes them to desert their calling and reveal to the world the 'truth'.
An Inquisitor from Rome and Templar Knights are sent to bring the deserters back. It is here they clash with Crowner who has already decided to help the runaways escape.
There is a subplot of piracy involving the Sheriff, John's brother in law, who decides to flex his muscles and lead the expedition to root out the criminals.
I enjoyed the twist in the ending, that saw Crowner caught in a trap of his own making.
From reading other reviews, perhaps not for dedicated aficiandos of the Medieval period, but I certainly found it an entertaining read despite the criticism that has gone before.