Sherwood is purely fictional. It takes creative liberties to weave an engaging tale, rather than being rooted in reality. So, don't expect it to be a true account of events.
The real story of Sherwood is likely to be about the Sherwood Forest in England. It is famous for being the legendary haunt of Robin Hood and his band of Merry Men. They were said to live in the forest, robbing from the rich and giving to the poor.
I don't think it's a true story. 'A Haunting in Sherwood' is probably just a creative concoction to thrill and entertain, rather than being based on actual events.