Cavalcando il fulmine

What is the connection between a Sioux Indian who died in the electric chair (and mysteriously came back to life without anyone being able to see him anymore), a ghost who haunts the house of the new client who landed at no. 7 Craven Road and John Haigh Christie, “the acid bath murderer” who really lived in the post-war period? The Nightmare Investigator has the task of finding out.