Some of the early victims find out all too late that the 40-foot Plesiosaur is not the placid, gentle giant that minds its own business paddling around the Loch as we've been told, but a rampaging monolith with an attitude that likes to waddle its way out of the water, wreck boats, roar like a foghorn, chase victims, bite them in half (it doesn't eat them whole, for whatever reason), dismember, decapitate, etc.
And it swam its way through some "undersea tunnel" (about 4,000 miles long?) from Scotland's Loch Ness to North America's Lake Ontario. No, really. It did. A vengeful scientist. a cross of Capt. Ahab and Indy Jones, wants to get even with the thing, having witnessed it devour his dad and two other men. The guy comes complete with all the clichés: an Australian safari hat, enough fire power to blow up a city, and he mumbles when he talks.
The movie plays like a remake of Lake Placid, which in turn was an apparent satire of Jurassic Park and Jaws type flicks. However, this one seems to want to take itself seriously. The actors play it this way, and make most of the characters work (even the clichéd ones).
The biggest problem was shoddy CGI. In one attack sequence, for example, Nessie decapitates its victim. Nessie's animation is so obviously pasted on to the picture it makes you laugh. Even phonier looking is the resulting "blood spray" which looks like somebody blew up a bottle of Cherry Soda (and pasted that in poorly, as well).
Decently entertaining, and at least it was free.