The fifth knight - E.M. Powell

To escape a lifetime of poverty, mercenary Sir Benedict Palmer agrees to one final, lucrative job: help King Henry II's knights seize the traitor Archbishop Thomas Becket at Canterbury Cathedral. But what begins as a clandestine arrest ends in cold-blooded murder. And when Fitzurse, the knights' ringleader, kidnaps Theodosia, a beautiful young nun who witnessed the crime, Palmer can sit silently by no longer. For not only is Theodosia's virtue at stake, so too is the secret she unknowingly carries—a secret he knows Fitzurse will torture out of her.

Now Palmer and Theodosia are on the run, strangers from different worlds forced to rely only on each other as they race to uncover the hidden motive behind Becket's grisly murder—and the shocking truth that could destroy a kingdom.