This is one of those films that looks a lot better on paper than it actually turns out to be.
It has a solid starting point for a thriller as eleven guests are invited for a weekend at an isolated country house, only to then be told by the hostess that one of them murdered her husband; the thirteenth figure is her somewhat odd son.
The assembled guests, hosts and servants
Admittedly this is clearly derivative of Agatha Christie. But, as the likes of Bava's Five Dolls for an August Moon and Michele Lupo's The Weekend Murders showed, an unoriginal scenario doesn't necessarily mean an unoriginal film.
Writer-director Javier Aguirre has also assembled a solid ensemble cast, with the likes of Patty Shepard, Jack Taylor and Simon Andreu amongst the guests / suspects and Paul Naschy as one of the servants.
Though more a metteur en scene than an auteur, Aguirre had some talent for horror, as demonstrated by his collaborations with Naschy on Count Dracula's Great Love and The Hunchback of the Morgue. And, indeed, the murder set pieces here, performed by a black-gloved and garbed killer using an assortment of hand weapons, are well executed, pun intended.
The trailer probably looked good, at least
So, where does it all go wrong?
The answer is in the pacing. The first twelve minutes are spent introducing the various characters. At thirteen minutes everyone settles down for dinner and the announcement that a murderer is amongst them is made. Dinner and conversation around this revelation, which everyone takes remarkably calmly, continues for another fifteen minutes.
Everyone then retires for the night, at which point Naschy's character goes to bed with the maid. Like the later hand to hand fight he engages in, it's a scene that crops up in almost every film he was in around this time, making one think it must have been a standard clause in his contract. As they make love, someone watches from outside, priming expectations that things are about to finally kick off.
Some rather obvious matte work
But nothing happens. Come morning everyone is still alive and quite happy to remain at the estate, digging out and divulging guilty secrets for the next half hour; by this point you may be wondering if Aguirre was intent on subverting the thriller by way of Waiting for Godot or The Exterminating Angel.
Two obligatory Naschy moments
Then, with half an hour left, we get two murders in the space of two minutes; a succession of three further deaths at regular intervals; a traumatic flashback; some further improbably calm reactions by those still alive and now proven innocent of the original murder, and a 'surprise' reversal with five minutes remaining. FIN.