Unlike many more enigmatically titled entries - Argento's Four Flies on Grey Velvet, Fulci's A Lizard in a Woman's Skin etc. - 1977 giallo from Ferdinando Baldi is one whose title tells you almost everything you need to know.
There are indeed nine guests for a crime.
The nine guests are members of a wealthy bourgeois family - the patriarch, his wife, their children and their respective partners - who go for a vacation at the patriarch's villa on an otherwise uninhabited island.
The crime aspect is more ambiguous, on account of the narrative being structured around an opening murder, shot through a gauze to connote its past / flashback status, followed by a subsequent And Then There Were None / Ten Little Indians / Ten Little Niggers scenario as the members of the family begin to be suspiciously killed off one-by-one.
The first thing that hurts the film as far as the mystery aspect is concerned is that the link between the past and present murders is not really made clear until comparatively late on. We see the victim being caught in flagrante with a woman, but not who she is, what happens to her, nor who guns the man down.
The second is that the identity of the avenger and the guilty parties amongst the group, in relation to this initial crime, are rather obvious to anyone who has seen the likes of Lupo's The Weekend Murders and Bava's Five Dolls for an August Moon and Bay of Blood.
Much like Dolls, the film sees a character apparently die and disappear, albeit without the immediate suggestion of foul play. Much like Bay of Blood - and D'Amato's Anthropophagous the Beast a psychically sensitive character foretells doom as she reads the tarot.
Unfortunately the opportunity for these same premonitions to create a more supernatural horror atmosphere is bungled. While we see the dead man trying to claw his way out of a sandy grave and the subsequent appearances of a zombie-like figure - curiously reminiscent of D'Amato's Erotic Nights of the Living Dead - the idea of an killer from beyond the grave cannot be sustained.
Whereas other gothic gialli like Crispino's The Etruscan Kills Again and Miraglia's The Night Evelyn Came out of the Grave and The Red Queen Kills Seven Times are careful to maintain a degree of uncertainty as to the nature of their monsters / murderers until the denouement, here the dead man and the zombie are interrupted by a more traditional wet-suited, black-gloved killer - albeit one who uses a pistol in disposing of two unfortunate sailors / employees.
Set pieces like this are reasonably well handed by Baldi, with the requisite hand held camera, racking of focus and zooms. Elsewhere there is plenty of gratuitous female nudity and J&B drinking. But if all the check-boxes are thereby ticked, what's largely lacking is the sense doing much beyond going through the motions, in taking an approach that is more personal or attuned to the specifics of the film, whether in a supportive or subversive manner.
The exception is Baldi's enthusiasm for shooting through grids and bars within the villa, useful both for conveying the entrapped nature of the characters and suggesting a visual connection to the opening scene insofar as it is filmed through gauze. These techniques also, however, again indicate a certain hesitancy in that, although none of the characters really being particularly pleasant or there to obviously identify with as investigator, the film-makers weren't willing to push things that bit more and play up their unpleasantness so that we wanted to see them really suffer, as with many of those in Bava's Greed Trilogy.
One thing the film definitely has going for it is a quality male cast, with Arthur Kennedy playing the patriarch and Massimo Foschi - particularly impressive - Venantino Venantini and John Richardson the sons and lovers.