陕北农村小男孩李天游出生以来从没见过妈妈，奶奶骗他是从月球来的，于是他认为自己是外星人，常常幻想和盼望能遇到飞碟，载他回月球找妈妈。当他看了神舟七号遨游太空的电视转播后，又迫切想成为一名宇航员飞上太空。80后城市女孩美音是某不靠谱摇滚乐队的 艺人助理，热爱声音，喜欢录音，在一次乐队穿越 黄土高原摇滚之旅的路途中，偶然听到天籁般的信天游，顿时开启了她尘封已久的心灵之窗。隐居荒漠植树防沙的传奇老人白马郎，身怀民歌绝技，原是受人景仰的 战斗英雄，他一直在寻找一个可以传承信天游的声音。信天游的歌声仿佛一根神奇的红线，把三个原本毫无关系的人逐渐紧密联系到一起。美音找到歌声的主人了吗？白马郎找到传人了吗？天游最终飞上太空了吗？他找到妈妈了吗？追随着信天游的歌声，超越想象的梦想之旅拉开帷幕，妙趣横生的成长故事娓娓道来。Lee Tianyou is a little boy brought up in the Shaanxi rural area, having never seen his mother. His grandma lied to him that he was an E.T boy brought to Earth from the Moon, which convinced him that he really was from the outer space and made him dreaming to take on a spaceship some day, get back to the Moon and reunite with his mother. When watching the Shenzhou VII Spaceship sent up into space, he determined to be an astronaut.Mei Yin is a metro girl and an artist assistant for a weird rock band. She loves sounds and recording them. She heard the heavenly Xintianyou folk songs during a road show on the Loess Plateau. She was greatly inspired at once.Mr. White Horse is a recluse occupied in planting trees to combat desertification turns out a legendary patriotic hero and folk song super singer. He is looking for someone younger to hand down the precious folk song art.