It's a hard time for young Angus MacMorrow. His dad is off at war, his mother struggles to keep the house in order, and there's a creature with horns, flippers, and very sharp baby teeth splashing around in the bath.

A kind of Free Willy set in Scottish lake country - Free MacWilly, that would be - The Water Horse: Legend of the Deep is a boy-and-his-beastie yarn with a Celtic twist. Adapted from a book by Babe author Dick King-Smith and directed by Jay Russell, of the family-friendly My Dog Skip and Tuck Everlasting, this World War II-era fantasy has its barmy charms, but also a kind of clunking cuteness that does it no good.

Alex Etel, one of the lucky brothers in Danny Boyle's Millions, stars as Angus, and he does a fair job of acting, and reacting, opposite what in its infant stages was an animatronic puppet, and in its full-grown form was all CGI. (Which means that on set, Etel was doing his emoting with a Ping-Pong ball where the mythical critter would be digitally rendered.)

The so-called water horse, christened Crusoe by Angus, was hatched from a football-size egg that the lad dug up on the rocky shore of the nearby loch, which happens to be Loch Ness.

At first Angus keeps his discovery to himself. But wee Crusoe doesn't stay wee for long, and soon Angus' sister, Kirstie (Priyanka Xi), is in on the secret, and then Lewis Mowbray (Ben Chaplin), the sullen, just-hired handyman, knows about the thing, too. Eventually, an entire squad of British soldiers on the lookout for German U-boats have to contend with the titular behemoth. The British Army should probably not use The Water Horse as a recruitment vehicle - the military buffoonery depicted herein reaches Monty Python levels of inept twittishness.

Emily Watson, looking at home in her '40s frocks, plays Angus' mother - coping not only with her son's obsession with what she believes to be an imaginary friend, but also with her own worry and grief about her husband at war. Brian Cox, pint in hand at a corner table in the local pub, narrates the yarn to a couple of backpacking college kids in the present day. His identity should come as no surprise to anyone - save a parent who nods off for long stretches of the film.

Very little of The Water Horse was actually shot in Scotland. The southern island of New Zealand - Hobbit country - provides most of the scenic backdrops, and Lord of the Rings maestro Peter Jackson rented out his digital-effects company to Russell and his crew. As a consequence, the film looks grand. A little too grand for the sappy proceedings.