The screenplay features more plot holes than a piece of Swiss cheese,and it borrows a bit from Agatha Christie's "Ten little Indians" aka "And then there were none" .And the flashbacks are clumsily edited in.For that matter ,the movie does not attain perfection ,as in Bava's earlier works such as "la Maschera Del Demonio" ,"I Tre Volti Della Paura" or "Operazione Paura".

Having said this ,Mario Bava was still quite capable of worthwhile directing in 1971.One can feel the huge influence he exerted over Dario Argento (whose screenplays were more complex and even more far-fetched ,but this is the kind of horror movies I ask more of) and over all the American "teenagers" thrillers of the eighties ,beginning with "Friday the Thirteenth" : the four young intruders' scenes set the pattern for all those gory flicks.

Mario Bava smartly used the "subjective " camera ,he makes us feel an invisible presence ,sometimes with an eye (a trick D'Argento will often use),sometimes with nothing:only the place , a disturbing character (Laura Betti and her tarots),or even innocent ones (the children in the trailer).James Bond's fans will be happy to see again Claudine "Domino" Auger ("Thunderball"),a former Miss France.

Bava used to cast "old" actresses too:Isa Miranda,who enjoyed a career both in Italy and in France portrayed the countess.Dario Argento,once more,would imitate him:in "Profondo Rosso" ,Clara Calamai made a stunning come back as Carlo's mother.