Robin Hood: Mark of the Black Arrow (Robin Hood: Demon's Bane Series)

A vast darkness is spreading. If left unchecked, it will engulf the world, and so Richard the Lionheart must depart England on a holy mission. In his absence, the safety of the realm is entrusted to his brother, Prince John. 

When the king departs, black sorcery begins to grip the land, threatening noble and peasant alike. Horrific creatures stalk the forests, yet the violence they commit pales when compared to the atrocities of men. A handful of rebels fight back, but are doomed to fail unless they can find a hero to lead them.