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Even the Loch Ness monster was a tot once, and The Water Horse: Legend of the Deep opens the fabled reptile’s baby book in search of life lessons and PG-rated thrills. Jay Russell also directed 2000’s My Dog Skip, so he has experience with unruly pets and damaged World War II veterans, which feature in both movies. Scripter Robert Nelson Jacobs (The Shipping News), adds some ruptured-family complications and a few wry touches to the story’s source, a reportedly bland book by Babe author Dick King-Smith. Despite these efforts, however, the film is as sterile and synthetic as most other recent flicks that star CGI beasties.

Told in flashback to a couple of American backpackers by a Scottish raconteur (Brian Cox), the story really begins with Angus (Alex Etel, the slightly annoying star of 2004’s extremely annoying Millions). While on a break from counting the days until his father returns from the war, Angus finds an egg in a tide pool; he stashes it in a shed on the estate where he lives with his housekeeper mother (Emily Watson) and older sister (Priyanka Xi). Later that night, during a storm, Angus hears sounds from the shed. He finds that a chirping creature—part puppy, part colt, part unshelled turtle, and a bit of giraffe—has wrecked the place.

The rest of the movie consists of Angus’ attempts to conceal his new pal and, once that fails, find him a refuge from closed-minded humans who assume the fast-­growing beast is a menace. Protecting the animal, which Angus dubs “Crusoe,” becomes much harder when newcomers arrive at the manor. First come some British troops, led by Capt. Hamilton (David Morrissey), an upper-class prig assigned to catch any German U-boats that might penetrate the area’s lochs and firths. (This nonjob, it’s suggested, is designed to keep him safe from real action.) Next is Lewis (Ben Chaplin), the new handyman, a brooding, war-scarred fellow. Being English, Hamilton is easily fooled (and will be, again and again). But Lewis is a Scot and soon discerns that Angus is hiding something. Fortunately for Crusoe, Lewis doesn’t freak when he encounters the beast. In fact, he recognizes it as a “river horse,” a creature from Celtic lore. Lewis becomes Angus’ ally, and together they help Crusoe when the silly soldiers mistake him for a U-boat.

Despite being anti-war, anti-adult, and anti-English, The Water Horse doesn’t fold a single major surprise into its jumble of ingredients. The movie is your basic a-boy-and-his-monster fable, competently done but untroubled by stuff that any 10-year-old might notice. (For example: Scotland is cold, but Angus takes a few underwater spins on Crusoe’s back without any symptoms of hypothermia.) Although the movie eventually makes a connection between Crusoe and U-boats, many of the set pieces could have been staged just as easily with a sheepdog as a sea monster. And Watson’s baffled, overwhelmed mom could have wandered in from a mid-’60s Disney family comedy.

The film does include a few amusing touches, though none of them are essential. Lewis angrily dismisses Hamilton as a “Sassenach” (a Scots word for English), and there’s a clever explanation of why the famed photo of the Loch Ness Monster had to be faked, even though the creature is real. That joke would be funnier, however, if The Water Horse ever persuaded viewers that Crusoe is anything more than a bundle of pixels.