As I Saw What You Did begins, the parents of teenaged Libby (Andi Garrett) and her younger sister Tess (Sharyl Locke) are heading out of town for the night and Libby's friend Kit (Sarah Lane) is coming by for a few hours to visit. Libby's parents had hired someone to stay with the girls but this sitter inconveniently cancels at the last moment, leaving Libby's parents with a decision to make - call off their plans and stay home or trust Libby to be in charge of the household. After some pleading by Libby, they agree to leave the girls alone in the remote, fog-shrouded house. It isn't long before Libby's parents have left, though, before Libby and Tess introduce Kit to one of their favorite past times - picking names at random out of the phone book to prank call.
Libby, Tess, and Kit burn up the phone lines for hours, cracking themselves up with each call. Putting on a deep, sexy voice, Libby asks for the man of the house by name if a woman should pick up - a tried and true bit that rarely fails to get a reaction. But as the night goes on, they adopt a new tactic. When someone answers, they say "I saw what you did and I know who you are." This proves to be a winner - except when they dial Steve Marak (John Ireland). In that case, it turns out to be the wrong thing to say because he's just murdered his wife (the act of uxoricide, as the film's posters noted in a helpful bit of vocabulary building).
An efficiently taut suspenser, I Saw What You Did plays out like an extended episode of Alfred Hitchcock Presents. Even though what these kids are doing is obnoxious, Garrett, Locke, and Lane are instantly, irresistibly likable. There's no malice in their behavior, just mischief. Sure, they're up to no good but not in a way where you're looking for them to get served their comeuppance. Garrett and Lane are personable heroines with Locke being the rare movie kid who isn't a grating presence. These three giggling girls make for good company and the idea of them being at risk becomes genuinely nerve-wracking.
As the movie's villain, John Ireland's Steve Marak is an atypical bad guy. He's not a psychopath, he's not a mastermind, he's just a guy who killed his wife (in a scene that's shocking in its violence for a 1965 film). And more than having to deal with Libby, Kit and Tess, Marek's biggest problem - outside of disposing of his wife's body - is fending off his romantically obsessed neighbor, Amy Nelson (Joan Crawford, who had just starred in Straight-Jacket for Castle). Whatever it is that Marak's got, Amy wants it bad. And she's not going to stop until she gets it. Crawford portrays Amy as desperate, needy woman and her dogged pursuit of Marak is enough to make this cold-blooded killer sympathetic. Ireland is a man of semi-mature years himself but Crawford was sixty at the time (and looking every haggard day of those years) and watching this boozed-up old bag refuse to let her last, best chance for a man shrug off her advances is an entertaining spectacle. Her confrontation with Libby, who she misconstrues as a romantic rival, shows that Amy might be capable of murder herself. No little tramp is going to get the best of this ancient beast and if she doesn't back off, Libby will have the claw marks to prove it!
Eventually, though, the nail-biting tension of Marak's love life takes a backseat to the game of cat and mouse between Marak and the girls and Castle makes the most of this climatic showdown. I believe that this film could play in any theater today and still have the audience on the edge of their seats. Whether in 1965 or 2009, it's not violence that scares an audience, it's the anticipation of violence and seeing characters they've come to care about placed in peril. Castle wrings plenty of suspense out of the final scenes without dragging the film out a second past where it needs to end. I Saw What You Did wasn't one of Castle's bigger successes at the time but I think it's dated better than some of his better-known titles like 13 Ghosts (1960) and The Tingler (1959). Garrett, Lane, and Locke didn't go on to bigger acting careers, sadly, but their chemistry and natural appeal give I Saw What You Did much of its charm.
Word is a remake is in the works courtesy of the My Bloody Valentine 3-D duo of Patrick Lussier and Todd Farmer (I Saw What You Did was actually already remade once in 1988 as a TV movie, directed by When A Stranger Calls' Fred Walton). And even though it sounds like a tricky proposition given today's technology, I don't think that the scares of I Saw What You Did need to stay in the age of rotary dial.