After returning from a year-long Moon mission, Cassie, a NASA botanist, finds herself in a remote cabin in the woods, where her estranged twin sister, Stella, a former NASA architect, has found a new life with her Earth Advocate fiancé, Bryan. As the sisters attempt to pick up the pieces of the rivalry that broke them apart, they grapple with perhaps the single biggest question that confronts humanity: is saving Earth still a possibility or should we commit ourselves to colonizing another planet?