Secrets and Mysteries. The Castle with Ghosts

1 riddle, 2 detectives, 5 chapters to find the solution.
Your first investigation!
When a mysterious murder occurs at North Bonny Castle, everyone suspects an evil spirit, and only Linsey, the young heiress of the Maclean clan, understands that something is not... right. The girl decides to conduct her own investigation and prove that there is nothing mystical about the incident. But where to start? How to become a detective if you've never solved a detective puzzle before? Linsey realizes that to get to the truth, she will have to delve into history. Join her investigation.
Question witnesses, jot down hypotheses, examine evidence. Outpace your literary rival and guess first who committed the crime.
Will you dare to join the game?..