The Bishop Must Die:

The twenty-eighth novel in Michael Jecks's medieval Knights Templar series. 1326: King Edward II's estranged wife Queen Isabella shames him by refusing to return from France to England. When the king hears she has betrothed their son to the daughter of the French Count of Hainault, all England fears invasion. The King's knights, including Sir Baldwin de Funshill, are commanded to London to protect the realm. Meanwhile Bishop Stapledon, the Treasurer of England, is under severe threat - but from whom? He has made many enemies in a long political life and Sir Baldwin and his friend, Bailiff Simon Puttock, must do all they can to find the would-be assassin before they strike...