Think Free Willy meets director Jay Russell’s own My Dog Skip. Snug and amiable, this is a comfy easy chair of a movie, based on the book by Dick King-Smith, and one easy to let yourself sink into and enjoy in spite of yourself: even a cynical grownup like me was quickly caught up in its effortless charm and innocent enthusiasm. Young Angus (13-year-old Alex Etel) is a shy, strange little boy living on the shores of a Scottish lake in the early days of World War II — Dad’s been off fighting for quite a while — and, well, a boy needs a friend, doesn’t he? This one finds a pal in the baby sea critter he rears from a pup as it grows from manageable just-post-egg-size to rather less hideable Loch Ness-monster-size. But still, the two local men — Ben Chaplin’s (Stage Beauty) roughshod groundskeeper and David Morrissey’s (The Reaping) snooty regimental commander — who are in an unspoken battle for the job of father figure to Angus can’t compare, as far as the boy is concerned, to the creature’s companionship. (Angus’s mom, playing by the always wonderful Emily Watson [Miss Potter], may have her own ideas about who should be filling her absent husband’s shoes.) The very minor detours into cartoonishness — most involving a bulldog named Churchill and comic animal chases — are more than outweighed by the surprisingly dark turns the film takes in its final act, ones that aren’t so much about how big and scary the monster gets but what terrible things the suspicious grownups try to do to it. The two little boys at my screening I spoke to afterward insist they weren’t scared, but they’d would say that, wouldn’t they?