The Killer Reserved Nine Seats starts out as a seemingly superior by-the-numbers giallo, with nine acquaintances (/friends who all hate each other) leaving a party to visit an abandoned theatre owned by the richest among them. In classic Christie-style, they quickly find themselves locked in for the night, with a masked assailant picking them off one-by-one. A strange man appears periodically to speak portentously about the history of both the theatre and the family of its owner, with the night's events seemingly inextricably linked to both.
The film initially seems to be inspired by the early scene in Four Flies on Grey Velvet in which Michael Brandon supposedly kills his stalker, witnessed by a strange masked figure watching from on high. The beautiful, but abandoned, theatre is used to good atmospheric effect, and the killer's mask is strongly redolent of the one from Four Flies. The subplot about the family history repeating itself every hundred years seems to be almost identical to that of The Red Queen Kills Seven Times (among other films), with the expectation being that the killer or killers is using the alleged family curse as a cover for their own nefarious actions. However, as the film progresses the whodunnit aspect of the plot is increasingly overshadowed by the cursed-history angle, to the extent that by the climax the film has morphed, insidiously, into an elegaic supernatural tale not unlike Lisa and the Devil. Accordingly, the film's mystery ceases to revolve around the identity of the killer or killers, but whether or not the increasingly prevalent supernatural aspects are indeed as they seem.
This is a highly unusual approach to take, with most other gialli which incorporate supernatural elements (Deep Red, Nothing Underneath) choosing to introduce said subplots right from the beginning of the films, which instantly redefines the environment in which the films take place, and allows the audience to focus on the giallo aspect from then on. In this instance, the giallo is subsumed by the supernatural, with the explanation/reveal of the killer being among the least convincing and most throwaway of the entire genre.*
The fact that the entire film, apart from a credit sequence drive, takes place in the theatre can be seen as both a strength and a weakness. The broadly similar Red Queen... takes care to contrast some extremely 70s apartment decor with the cobwebby, old-world castle which is apparently the locus of the film's curse. This focus on the contemporary is reflected in the film's ultimate debunking of the curse. By refusing to allow any glimpse of the outside world and its then-garish decor, The Killer Reserved...'s director Giusepe Bennati creates a hermetically sealed environment within which we can believe in ghosts and family curses. On the other hand, because we are denied any depiction of the outside world, the intrusion of the supernatural elements can grate a bit. Consider Lisa and the Devil, a film with which The Killer Reserved... seems to have little in common until the very end; the journey Lisa takes in the car is of paramount importance, as the thick fog and black of the night come to represent her journey between worlds. By denying us the pleasure of such a journey, and refusing to initially foreground any supernatural aspect of the film's plot, Bennati changes the focus of the film's mystery, almost uniquely within the genre. Instead of speculating as to the killer's identity, by the film's end we are instead wondering whether the curse is in fact real, and whether the film does indeed take place in a world at the mercy of supernatural forces. It's an experience every bit as surprising, frustrating and refreshing as that sounds.
*One scene in particular seems totally illogical, and may annoy audiences on repeat viewing. Part of the fun of these films is trying to guess the killer whilst watching the film unfold, and viewers engaging in this pursuit will be constantly absorbing information and refining their choice of killer. When a scene seems designed solely to throw such viewers off the scent through the use of misinformation and extremely illogical dialogue and behavior, it can leave a sour taste. Misdirection is fine, to be encouraged even, but having two characters speak alone in a manner which suggests that they have no idea what's going on, when in fact they have masterminded everything up to that point, is Not Cool.