The 10-year-old hero at the center of the film “The House With a Clock in Its Walls” likes to look up words in the dictionary, like “foreboding” and “indomitable.” He might want to be familiar with the term “execrable” — that’s a good one for this movie.

Adapted from the 1973 John Bellairs young adult supernatural thriller, the film somehow manages its own witchcraft in finding the perfect un-sweet spot — it’s too scary for little kids, not scary enough for older ones, not funny or clever enough for their parents, and too redundant for everyone. Poof! Watch the audience disappear.

Horror specialist director Eli Roth has stumbled badly as he enters the dangerous realm of whimsical, which is added here at such high doses as to be lethal. The film is ostensibly a Harry Potter-lite coming of age yarn, but the real spooky thing is why Cate Blanchett and Jack Black decided to tag along.

The story — by Eric Kripke, creator of TV’s “Supernatural” — centers on a recently orphaned 10-year-old boy named Lewis in 1955. He moves to a Michigan town to live with his mysterious, chocolate-loving uncle, played by Black, who turns out to be a warlock. The next-door neighbor, Florence Zimmerman, is an elegant, purple-loving witch played by Blanchett.

“You’ll see. Things are quite different here,” Black’s character says to the astonished boy. But he’s lying — things are very familiar here: foggy graveyards, creepy dolls, dusty books, animal skeletons in small carved boxes, ornately carved book jackets, secret rooms behind bookcases, thumping in the walls and even comedic non-human sidekicks (this time an armchair and a topiary griffin).

There’s been an obvious attempt to ape the chilly menace of Edward Gorey, who supplied images for Bellairs’ book, but this movie really just leans on props and suggestive music, never finding a consistent tone or vision. Sometimes it feels like a Wes Anderson film, at others it goes more like Wes Craven.

Young Lewis, uptight, precocious — and outfitted in the laziest way to show that, with a pair of WWI-era aviator goggles and a bow tie — must learn to be a warlock himself, fit in at school, solve the mystery of the hidden clock and save the universe. Child actor Owen Vaccaro does admirably here. It’s the adults who have let him down.

Foremost among them is Black and Blanchett, who are in different movies — he’s in a comic farce complete with butt jokes and vomiting pumpkins, and she’s doing some very serious English drawing-room drama. “It’s the nuts that make things interesting,” she says at one point. “I’ve found that all one really needs in this world is one good friend,” she tells Lewis primly.

Toward the end, Blanchett arms herself with a weapon resembling an umbrella, becoming a sort of Oscar-winning Mary Poppins as she mows down enemies with what seem to be bolts of lightning. What happens to Black? Would you believe a truly disturbing sequence with his bearded adult face on top of a baby body? (There’s an image we’ll all take to the grave.)

This whole mess drags itself to a messy conclusion — wait, is that Kyle MacLachlan making an appearance late on? Kyle? Did you lose a bet, too? — and then it all ends on an impossibly sticky, sweet big wet kiss of a finale that undermines the entire project.