Houston, 1975. A new Apollo mission launches into orbit, on course to dock with a Russian Soyuz craft: three NASA astronauts and three cosmonauts, joining to celebrate a new dawn of Soviet-American cooperation. But as NASA Flight Controller Kaz Zemeckis listens in from Earth, a deadly accident changes everything.

Meanwhile, from a remote location in east Asia, the first Chinese spacecraft secretly launches. On board is China's first astronaut, Fang Kuo-chun, whose mission puts him on a collision course with the Apollo crew. As Kaz races against an enemy on the ground and for answers beyond the sky, the safety of the remaining crew hangs in the balance .