Texas, 1981. A girl named Hang is riding a bus to Amarillo. Queasy from a heavy breakfast and the bouncing ride, she gnaws a chunk of bitter ginger root. The harsh taste comforts her. Texas is an unknown, vast and strange, but as readers of Thanhha Lai’s searingly beautiful BUTTERFLY YELLOW (Harper/HarperCollins, 284 pp., $17.99; ages 12 and up) will soon learn, Hang is a refugee. She is familiar with bitter things.

Lai, the author of the National Book Award– and Newbery Honor-winning “Inside Out & Back Again,” tells a story that begins in the spring of 1975, in the final days of the Vietnam War, when Hang made a terrible mistake. She was 12 and living in Saigon. Her family was desperate to flee the city before it fell to the North Vietnamese. The newspapers were full of stories about Americans airlifting orphaned children to safety, so Hang took her small brother, Linh, to the airport and pretended they had no parents. She was certain they would both be taken to America and that her family would somehow follow them, but only the youngest children were being rescued. Linh was ripped from Hang’s arms and carried, thrashing, onto an airplane. Hang was left behind holding nothing but a card bearing an Amarillo address.

From that moment on, the anguished Hang has only one goal — to get Linh back. Six years later, she arrives in Texas. Helped by a wannabe cowboy named LeeRoy, Hang finds her brother, but the reunion is a disaster. Linh is David now. He’s older and wants nothing to do with the strange girl standing on his doorstep. He barely remembers his family. “They had become vapors, shapes he couldn’t catch. He did remember their smells. Ba was mint, Father ash, Mother flowers and sister ripe fruit.”

Devastated, Hang vows that “Linh will remember. Memories will return on his tongue.” But with her brother having forgotten his Vietnamese, and Hang speaking little English, language — like a treacherous sea — becomes yet another barrier she must cross.

Words, however, push through. Spoken, written, whispered or sung, they connect. Hang may not always know their exact meaning, but she feels their intent and uses them to forge a path to skittish David; to Cora, David’s American mother; to blustery LeeRoy; and, finally, to her driven, damaged self.

For Hang, too, must remember. She has survived a wretched life under the North Vietnamese — one of hunger, fear and loss — only to make a harrowing passage across pirate-infested seas in a flimsy fishing boat. War, using its own brutal language, has written some of its torments on her body; others it has etched into her soul. She cannot bear to tell her own story, not even to herself.

Bit by bit, in broken English and Vietnamese, Hang shares stories of Vietnam with David. She reminds him of the sweet and sour fruits he used to enjoy. She sings him a song he used to love about a buom vang, a yellow butterfly, hoping he’ll sing it with her. Eventually, in one of the most moving passages in the book, he does.

Hang, David and LeeRoy are riding a Ferris wheel at the county fair. As the wheel turns, a yellow butterfly lands on David’s hand, which is sticky with melted popsicle. Hang sings the butterfly song again and at last David joins her. LeeRoy knows the melody, too. To him, it’s “Frère Jacques.” By the time their car reaches the top, all the kids are singing — in Vietnamese, English, French and Spanish — and the words of a sweet, silly childhood song become a bridge, one Hang uses to make her way across the deep gulf of time to her brother.

In this lovely, luminous scene, in this radiant pearl of a book, Lai shows that we human beings — fragile or strong, saved or doomed, frightened or brave, and sometimes all of those things at once — are singing the very same song: a song of grace and redemption, a song of courage, a song of hope.