No that isn’t a typo and no this isn’t the 1993 Argento film.
Rather, Trhauma is the actual title of this 1980 giallo-slasher entry from Gianni Martucci and Alessandro (“Al”?) Capone.
The story begins with a prologue, recalling Halloween, Friday the 13th and, indeed, Nine Guests for a Crime: One boy convinces another, who seems to be be blind in one eye, to climb a tree, which he then falls out of with apparently fatal results.
Following this we cut to the present as a group of bourgeois types arrive at a holiday home in an isolated area. Soon two of them, a photographer and his model, wander off to do some shooting. After they become separated, she’s killed by one-eyed jack, now a man.
Less than ten minutes in and we have a naked woman
The others are concerned about her absence, but don’t do anything about it until it’s too late and the phone lines have been cut. As the killer closes in and the body-count rises, we learn some of their secrets, including gambling debts, lesbian affairs and blackmail.
Franco Diogene prepares to enter the pool and the water prepares to leave
Eventually a final girl/woman is identified and a tense extended stalk and chase scene ensues. The abrupt resolution and closing epigram, however, seem more giallo than slasher, bringing things back full circle.
An unpretentious and effective little film that doesn’t outstay its welcome and delivers on suspense, shocks and sleaze and sees the filmmakers make good use of their locations.