A European village is alarmed by a number of unexplained deaths that the local police are unable to solve. The authorities call in Inspector Doren of Interpol, and the only clue the Chief Constable can give the detective is the fact that, each time a murder was committed, the electric lights in the whole neighborhood went out. The locals believe that the killings of the young girls are linked to the vague shadows in the caves under the local castle and to the mysterious Curse of the Green Eyes. They distrust the inspector and offer no assistance when still another murder takes place at the village inn---in the room next to that occupied by the inspector---and the body disappears. There are many suspects: the chattering innkeeper; the mysterious Professor Adelsberg; his manservant John ; the deaf-and-dumb Tom; and the inscrutable doctor, who has been issuing strange death certificates. Doren moves to the castle, where Professor Adelsberg is carrying out some scientific studies. There he meets the Professor's pretty assistant Karin. She is marked as the next victim.