This had potential, and it actually did realize some of it. However, the dialog is hard to hear in places, and the editing is just bizarre, several times jumping from a tense moment straight to another scene without resolving anything.
My biggest objection, though, is more fundamental: for the first two-thirds or so of the movie, the fascinating "babysitter" seems to have some kind of supernatural... something. It's never clarified what, but she seems to be almost mesmerizing people on occasion; at another moment, she is unfazed by a car nearly hitting her, almost as though she is in control of the situation more than the driver is. Then in the last third or so, that "something" seems to vanish and she is just a crazy young woman.
Zimbalist is captivatingly beautiful here and seems game to bring her character to life, and the other players are all fine in their roles. However, the story just doesn't quite make sense in spots and the relationships feel hurky-jerky. A bit more time invested into the writing would have helped, as would a better job on the sound mixing and the editing. Lacking those things, I can only give this a 4, as I ended up just wondering what the point of this was. Still, if you're a fan of stalker/psycho movies, or of Shatner or Zimbalist (or anyone else here), you will probably enjoy this at least a little bit.