Crossbows and Crucifixes by Henry Garnett

In this story, set in 1585 England, the author tells the tale of a supposed group of "priest hunters" and an armed resistance of Catholic people. The main character Nicholas discovers that his mother has converted to Catholicism and he joins too, quickly becoming involved in a group called the Companions whose purpose is to lead and protect priests from place to place so Catholics can receive the sacraments.