Nick's downstairs with me now, smoking and talking to the cat - oh wait, he's buggering off upstairs again. Huh.
Another Italian film here, so you know you're in for something... interesting.
An American jazz musicial living and working in Rome sees a woman being brutally murdered in her apartment. The woman was a psychic who, earlier in the day during a demonstration, had picked up on the mind of a killer, and it's this killer who later came to silence her. Racing to the woman's apartment to try to save her, the musician arrives to late but seems something unusual there that he later can't quite put his finger on. With the help of a pretty journalist with a dodgy car, he sets out to solve the mystery, while the killer continues to get rid on anyone who could expose their identity...
Dario Argento's films generally have a set theme: the protagonist is nearly always an American working in Italy, he has a glamourous girlfriend, and the killer is nearly always from the same... group (trying not to give too much away here). This can mean that if you've seen one Argento film, you've seen them all, but I disagree. The giallo films are the equivalent of the pulp novel (and are indeed named after the Italian version, where the books are all yellow), and so while it might be fun to try to work out the plot, you're really just supposed to sit back and enjoy the show.
Argento is also one of those directors who has the charge of mysogeny thrown at them, because he sometimes tends to stereotype certain types of female and lingers maybe a little too long on the torture and murder of pretty girls. Again, I think this is more of an Italian cultural thing. although I'm always open to correction on this...