All the way through Ponyo (Walt Disney Pictures), the astonishing new animated film from Japanese legend Hayao Miyazaki, I puzzled over how I'd ever be able to outline the movie's plot in review form. You see, there's this goldfish-girl named Ponyo, or sometimes Brünnhilde, who lives in a bubble under the sea with her wizard father. Ponyo/Brünnhilde looks less like a goldfish than like a limbless baby doll in a dress, and, oh yeah, she's constantly surrounded by dozens of baby sisters who look like miniature Ponyo replicas, all of whom can transform at will into enormous fish. Then one day Ponyo (voiced by Noah Cyrus, Miley's little sister, in this English-language release) swims ashore, drinks the blood of a human boy, falls in love with him, and decides to become human herself … but her semi-completed transformation somehow throws the ocean into chaos and causes the moon to come dangerously close to the Earth, a wrong that can be righted only by consulting with the Goddess of the Ocean (Cate Blanchett) in an underwater nursing home.

Even that wordy and incoherent summary leaves out multiple story threads, crucial characters, and visual conceits (like the propeller-powered submarine that the wizard rides around on, the hundreds of rainbow-colored jellyfish that Ponyo must swim through on her way to the surface, or the magic droplets that, when thrown on the ocean's surface, transform into menacing waves with eyes). I walked out of the movie determined to dispense with plot altogether and publish a peremptory micro-review: "Just see Ponyo." But then I went home and told the story to my 3-year-old daughter, who immediately understood it (and who volunteered to right the sea's chaos herself as, without a trace of cognitive dissonance, she devoured a fish dinner). The fact that a child can grasp its logic doesn't mean that Ponyo is a kids' movie—in fact, many of its themes and images may be too intense for younger children. It means that Miyazaki is a great artist, able to tap into a part of his mind that most grownups (including artists) have long ago closed off. Ponyo is baroquely and extravagantly weird, yet its story has a mythic simplicity: Boy meets fish-girl, boy loses fish-girl, fish-girl risks upsetting the cosmic order to get boy back. It's Hans Christian Andersen's The Little Mermaid, with less sacrificial suffering and more ramen noodles.

The undersea realm where Ponyo dwells with her misanthropic father (Liam Neeson) is dazzling in its beauty and complexity, but the realistic world above sea level is no less meticulously rendered. Sosuke (voiced by Frankie Jonas, the youngest Jonas brother), the little boy who befriends Ponyo, lives in a house perched on a cliff that seems to exist in perpetual dialogue with the sea—sometimes literally, as when Sosuke's seafaring father, Koichi (Matt Damon), uses his ship's light to send signals to Sosuke and his mother, Lisa (Tina Fey, dryly witty as always). Koichi travels so often that Lisa is, for all practical purposes, a single mother, overworked and crabby but devoted both to her son and to the old women at the retirement home where she works (a Greek chorus of crones marvelously voiced by Lily Tomlin, Cloris Leachman, and Betty White). The last thing Lisa needs is another child to care for, let alone one who's capable of creating global weather disturbances. When Ponyo, her fish-to-human transformation only half-completed, moves into their home against the wishes of her father, Lisa's resourcefulness and her son's courage are put to the test.

Ponyo has elements of both a classic fairy tale and an environmental message movie, but it shifts as nimbly between those genres as Ponyo herself does from person to goldfish and back again. Miyazaki's view of the relationship between the human and natural worlds is a profound and ambiguous one. Though Ponyo is, in part, an ecological fable, its message goes way beyond "Don't litter, kids." Ponyo's love for Sosuke horrifies her environmentalist father, Fujimoto, who blames humans for polluting the world's oceans. But despite its sympathy with Fujimoto's cause, the movie ultimately comes down in favor of fish/human miscegenation. Miyazaki, whose films often take place at the border between the human and the natural, has said that "we need courtesy toward water, mountains and air in addition to living things. We should not ask courtesy from these things, but we ourselves should give courtesy to them instead." In Ponyo, that courtesy is expressed as love, not only between Sosuke and Ponyo but between the inhabitants of the earth and the creatures of the sea.

Slate V: The critics on Ponyo and other new releases