I first saw Tenebr(a)e under the moniker "Unsane" (which is supposedly missing ten minutes of gore and some extensive camera-work). I really enjoyed the film, so I bought the rerelease print from Anchor Bay, and I must say, the restored, uncut, letterboxed print looks and sounds wonderful.
There's no need to go into the plot other than to say Anthony Franciosa stars as American horror novelist Peter Neal and, while he's in Rome on a book tour, murders are being committed by one of his crazed fans. I read somewhere that Argento is king of stringing together a plot and cheating audiences just so they can't guess the identity of the killer, and with this as evidence, I agree 100%. It's nearly impossible to figure out this plot before it's fully explained.
Luciano Tovoli's camera-work/cinematography is brilliant, especially the luma crane shot (which goes up one side of a building, over the roof and down the other side in one unbroken taken). There's also an extremely well-photographed and directed sequence featuring a girl being pursued by a rabid Doberman. Now they would do those two scenes with computers, and I think that obliterates the charm of the hands-on film-making process.
In short, this film puts Hollywood thrillers like "Copycat" "The Bone Collector," and "Se7en" to shame, and it's apparent all three films stole ideas from this one (and from other films in Argento's oeuvre).