Everyone knows that if you don’t have anything nice to say, you shouldn’t say anything at all. Less well known is the adage: “You can’t publish a movie review that is entirely blank.”

When it comes to “Dolittle,” that’s too bad.

In the new movie inspired by the Doctor Dolittle books, we first meet John Dolittle (Robert Downey Jr.) in an animated introductory sequence, lovely enough to be promising. The doctor can talk to animals — a skill he has learned, not an innate ability — which leads Dolittle to establish a veterinary hospital for patients with physical and psychological problems. But ever since the disappearance of his explorer wife, who went missing while on an expedition to find what’s known as the Eden Tree — said to be able to cure any ailment — Dolittle has closed his doors, shutting himself off from the world, save for a few animal friends.

Those doors open a crack when a tenderhearted boy named Tommy (Harry Collett) accidentally shoots a squirrel. Poly the parrot (voice of Emma Thompson) leads Tommy to Dolittle’s manor home — which must smell like a giant litter box — and convinces the doctor to treat the gunshot victim.

Shortly afterward, an emissary arrives from Buckingham Palace, summoning Dolittle to the bedside of Queen Victoria (Jessie Buckley), who is near death from a mysterious illness.

Because without that tiny plot point — on which the fate of Dolittle’s estate hinges — Dolittle, Tommy and the chattering menagerie wouldn’t have a reason to set off on their own adventure to find the legendary tree. Hanging about Victoria’s bedside are a courtier (Jim Broadbent) and a physician to the queen (Michael Sheen), neither of whom seems all that upset over the possibility that the monarch may die, as her death would mean more power for them.

So begins a frenetic quest to find the magical tree. So frenetic, in fact, that during the sprint across the seas — wherein a frigate, with Sheen’s menacing Blair Müdfly aboard, threatens Dolittle and company — none of the pit stops along the way generate any suspense whatsoever. Those stops include an island ruled by the angry (and vaguely Arab) King Rassouli, played by the entirely non-Arab Antonio Banderas. Throw in some fart jokes and a constipated dragon, and you’ve got yourself a movie.

In the title role, Downey adopts a Welsh-like accent, which seems to be all the effort he could muster for this performance, which alternates between dull and manic, despondent and quirky. All of the other characters, including the CGI animals, are almost completely forgettable.

Sheen is the only performer who embraces the inherent campiness of the story, and he alone makes his character’s motives at least somewhat understandable. The large voice cast — a group whose pile of acting nominations and awards would rival the size of Chee-Chee the gorilla (Oscar winner Rami Malek) — shows how acting ability doesn’t necessarily translate to voice acting. “Dolittle” is mostly just a game of “Whose voice am I hearing now?”

As for the animation, it’s fine in close-up, but whenever a CGI critter appears in the same frame as a human being, man and beast don’t seem to be occupying the same screen. Or planet.

Or dimensional reality.

Ultimately “Dolittle” is not just a weak story, badly told, but a puzzling waste of talent. (The only silver lining? A relatively fleet running time.) Here’s hoping the cast bought themselves something nice with the money they made. Though, to be honest, the only decent thing to do with it would have been to distribute it — a kind of movie malpractice award — among this doctor’s real victims.

PG. At area theaters. Contains some action, rude humor and brief coarse language. 101 minutes.