Perdita And The Midsummer People

First there is a lady chained to a birch tree, and then Perdita sees a huge White Horse where there isn't one, and then there is a farmer ploughing dangerously close to a fairy ring ... And the wild Midsummer festivals are coming closer and closer ... This is the second of the Perdita novels, and the book includes a long short story 'What Didn't Happen at Samhain'.