The Stonehenge Sacrifice — Susan Hart

The Stonehenge Sacrifice is about an American university professor, whose entire life is wrapped up in Stonehenge. She takes her daughter to England to enjoy the Summer Solstice at the monolithic site on the Salisbury Plains. A murder sidetracks them from their rental car and they decide to hook up with the very eccentric owner of a Stonehenge-themed traveling carnival. After the daughter meets the owner's bizarre family and sees how her mother is starting to get very friendly with him, she decides that she wants to be anywhere but heading up to experience what she thinks will be either a dry lecture on Stonehenge, or a bunch of weirdos dancing around a fire pit. It turns out to be anything but.