"Young Sherlock Holmes" is the latest product off the Spielberg assembly line (he's the executive producer) and bears its machine-marks. For all that, though, it's a perfectly agreeable family entertainment, a craftsmanlike fantasia on Conan Doyle.

The movie takes place at the height of the Victorian era (meticulously re-created by production designer Norman Reynolds); the consummate detective and his stout-hearted sidekick, Watson, are still boys. When Watson (Alan Cox), pudgy and bespectacled, transfers to a new school, he's given the bunk next to young Holmes (Nicholas Rowe), who promptly rattles off Watson's name, where he's from, what his father does and what his favorite food is (custard tarts), all through his soon-to-be-fabled process of deduction.

The kinks aren't worked out yet, in either the deduction (he pegs Watson as James, not John) or the violin, at which Holmes saws ineptly. But already he's forging the familiar persona, and much of the fun of "Young Sherlock Holmes" comes in the way screen writer Chris Columbus ("Goonies," "Gremlins") builds the origins of all the Holmes paraphernalia into his story: the deerstalker hat, the Inverness coat, the meerschaum pipe, the "Elementary, my dear Watson." (Everything but the cocaine addiction.)

If Columbus has a way with props, though, he's less successful with narrative; he still seems to have learned his screen writing from a roller coaster. Holmes sees a pattern in a series of deaths and suspects foul play; investigating, he discovers an underground cult of Egyptian devil worshipers (Isis, actually), whose murderous secret is a dart tipped with a hallucinatory chemical -- the hallucinations drive the victims to suicide.

Along with his girlfriend Elizabeth (Sophie Ward) and, of course, Watson, Holmes sets about foiling the cult. The Egyptians are there so that "Young Sherlock Holmes" can have its required "Indiana Jones"-style set pieces, complete with huge gilded icons, virgin sacrifice, chanting, unpleasant-looking liquids and scores of shaved-head extras. The only thing missing is Spielberg, whose genius for moving the camera brings this kind of set to life -- he packs information into his frame like shotgun pellets and blasts it out at you. Here, the man behind the camera is director Barry Levinson, whose static compositions make the sets seem phony and expensively overproduced.

But Levinson has learned some of Spielberg's technique for filming action sequences -- the hallucinations in "Young Sherlock Holmes" are spectacularly staged, the sequences composed with a Spielbergian flair for disorientation, full of quick-cut montage and off-kilter framing. And the special effects (by George Lucas' Industrial Light and Magic, with a nod to Ray Harryhausen) are ingeniously frightening and appropriately low-tech -- a roasted capon, for example, that sprouts a viciously pecking head, or a bloody crusader who springs to life from his stained-glass window.

Levinson, the director of "Diner," has a way with actors. You need only look back at "Goonies" to see how bad child actors can really be, but Rowe, aquiline and arrogant, moves with a nice aplomb here, and Cox is a comic gem as Watson -- rolling his eyes, chewing slowly on an idea (or an eclair), he's a kind of walking shrug.

"Young Sherlock Holmes," though, is neither an actor's nor a director's piece, but a writer's, and something of a triumph for Columbus, who is much maligned, partly because of his age (he's 27), more justly for his weakness for gimcrackery.

But each of Columbus' scripts has been stronger than the one before and in important ways. He has learned to filter his gags through character -- there's a hilarious sequence in which Watson, suffering a hallucination, is assaulted by animated cream puffs and eclairs; Holmes' best lines work because of the characterization of his adversary Lestrade, not yet Inspector Lestrade, but already a pompous bore. And Columbus understands the importance of construction, of laying the foundation for what follows. His script for "Young Sherlock Holmes" is, if anything, over-constructed -- there's hardly a thread that isn't picked up later. But in the Reign of Slapdash, in which few filmmakers seem to feel movies have to be constructed at all, that's hardly a sin.

Young Sherlock Holmes, opening today at area theaters, is rated PG-13 and contains violence.