Sherlock Holmes and the Lone Tree Assassin

Sherlock Holmes is asked to solve a case. This case is...interesting, however. It was requested by a young woman at the approximate age of 20. Her father was ruthlessly murdered, but there is no evidence. Nothing. No marks or anything. All that's left is a burn mark in the shape of a tree. Sherlock precepts this as an easy case and brushes it off. Three days later, twelve people have been murdered. No marks except a burn mark shaped like a tree. Things are getting very suspicious. Not knowing what else to do, Sherlock takes the case. He knows these methods are very familiar, but he does not remember, and for him, it's a new experience. As the time grows, his memory is fading faster and faster. Soon, all he remembers is the girl. He doesn't even remember his own name. All he remembers is the girl. But why? Why her?
Find out. Who is the lone tree assassin?

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