HarperCollins. 507 pp. $26.99

Readers who have waited years for another novel by this beloved American author will devour this one. Something dark is hidden inside it, but many won't realize what they've swallowed until long after the last page is digested.

So much of this story is true, from the lives of Mexican painters Frida Kahlo and Diego Rivera to the exile and assassination of their Russian friend Leon "Lev" Trotsky, from the internment of American citizens of Japanese descent during World War II to a hundred other hypocrisies of U.S. administrations from Hoover to Truman.

The novelist's fans will follow her willingly, but read Kingsolver for her fiction, not for history writing. She aims at a deeper truth and provides likable narrators, embedded in textured prose, to guide us to it.

In The Lacuna, our guide is Harrison Shepherd, a half-Mexican, half-American boy whose gold-digging mother, Salomé, has dragged him to an island off the coast of Mexico to live with one of her lovers - the first of many men who won't quite "produce the cash" after she's left the Washington bureaucrat who fathered her son.

Unable to act, Harrison observes and records: "Everything about Salomé came from a jar or a bottle: first, the powder and perfume, the pomade for her marcel wave. Next, the headache, from a bottle of mezcal. Then the cure, from a bottle of Bellans Hot-Water Relief. Maybe some other bottle gave her the flapper-dancing, crank-up-the-Victrola Twenty-Three Skidoo."

The mother flaps, hopelessly, at semi-eligible men while the son swims into a hole in the sea cliff - also a lacuna - that leads through a cave to another world.

Half-drowned, the boy discovers an Aztec ruin. He has surfaced in the jungle amid stones "piled like a sand castle underwater, with bits of shining things mixed into the pile." Gold coins, perhaps, or leaves. But there are also leg-bones wedged into the rocks, for this jungle pool tells of blood and sacrifice as much as hidden treasure. There's "no good way to walk out of there. And no good way to swim back out of that cave, either," until the strong ocean tide pulls him out of the cenote, "dragging a coward explorer back from the secret place, sucking him out through the tunnel and spitting him into the open sea."

The mother cuts and runs again, and the boy resurfaces in Mexico City. The city lies like a Spanish veneer, a palimpsest, over the Aztec realm once ruled by Monteczuma. The Aztecs sacrificed virgins to their gods, but Cortes slaughtered the Indians wholesale. A lesson: True friends are rare and trust is oft misplaced.

Of Harrison's friendships, the one he forges with Frida Kahlo lasts a lifetime. The boy mixes plaster as well as he makes bread dough, and Kahlo's famous husband, the mural-maker Rivera, has hired him. However, it's the little Indian queen who truly sees him as he is, as he does her:

"Señora Frida is a confusion of terms: sometimes like a stern little man, then suddenly a woman or a child, but in every form demanding that you remain in love with her. Commanding even her giant of a husband, until he runs off to be rescued by softer, pillowy women. . . . [Her] cat smile, those hands, the paintbrushes. Any one of them can be like a slap across the chest."

Kingsolver rescues Kahlo from any interpretation of her as a victim of Diego. Instead, the novelist paints the artist as a force of a nature, a woman who had her lovers, too, including her cherished guest, Trotsky.

As far as history goes, the Mexico sections describing the exiled enemy of Stalin and his hot-blooded painter pals had this reader riveted. But by the time Harrison, himself ultimately a historical novelist, is being interviewed by the House Committee on Un-American Activities, the weight of documents has overwhelmed the vivaciousness of the characters. Too much research, apt though it is, slows the book down, just as too much flour weighs down the dough, suffocating the airy lightness of the bread.

Over the years, Barbara Kingsolver has continued to thicken her plots and lard them with history. After The Poisonwood Bible and now this novel, it's hard to remember that her first and deeply satisfying novel, The Bean Trees, was such a simple confection. Still, she began it with the same ingredients: an orphan and a motherly friend, a young American transformed by a Latin couple.

Nowadays, Kingsolver's plots contain so many ingredients, so many layers of sweet and savory events, people, and secrets that a reviewer is hard-pressed to identify just what the point of the recipe is. Perhaps it's this: History repeats itself, but we don't remember, so we let bad things happen again.

We don't remember because Americans have amnesia when it comes to our fears: foreigners and homosexuals, dark-skinned people and non-Christians. Our tendency is to punish the ones we fear, whether they've done anything to harm us or not.

Americans seem doomed to repeat the paranoid history we can't remember, and our inability to remember is yet another definition of lacuna, one that Kingsolver never mentions, but her novel exemplifies.