Tomas and Martin are a gay couple living in Paris whose marriage is thrown into crisis when Tomas impulsively begins a passionate affair with young schoolteacher Agathe. But when Martin begins an affair of his own, Tomas must confront life decisions he may be unprepared—or unwilling—to deal with.

In the 28th century, Valerian and Laureline are special operatives charged with keeping order throughout the human territories. On assignment from the Minister of Defense, the two undertake a mission to Alpha, an ever-expanding metropolis where species from across the universe have converged over centuries to share knowledge, intelligence, and cultures. At the center of Alpha is a mysterious dark force which threatens the peaceful existence of the City of a Thousand Planets, and Valerian and Laureline must race to identify the menace and safeguard not just Alpha, but the future of the universe.