He who whispers

The war is over, and the Murder Club is set to reunite in London. However, only Miles Hammond and a mysterious woman named Barbara Morrell arrive to hear Professor Rigaud's strange tale. He recounts the impossible death of Howard Brookes, stabbed atop a tower with no apparent way for the killer to reach him. All signs point to Fay Seton, but the only explanation for her involvement seems to be supernatural. Can Dr. Gideon Fell solve this baffling case?