Mad as a Hatter: The F.B.I. shows up on the doorstep of Graymoor Mansion looking for Marshall, but they aren't seeking to arrest him. They've come to hire him. Over a period of weeks, a series of murders have been committed that all have one thing in common; the victims were discovered in rooms locked from the inside with no possible exit for the killer. After eliminating all natural possibilities, only the supernatural remains and who better to investigate...