In 2032, Ryland Grace awakens from an
induced coma on an
interstellar spacecraft. Initially erratic and
amnesic, Grace learns that he is the sole survivor of the three-person crew, on a spaceship
light-years from Earth. Grace remembers that he is an American
middle school science teacher and former
molecular biologist. Years ago, scientists observe an
infrared line, named the "Petrova Line", forming from the Sun to
Venus. They discover a
microorganism, termed "astrophage", proliferating on the Sun's surface, causing it to dim, and predict it will cause catastrophic
global cooling within 30 years; Government agent Eva Stratt recruits Grace and other scientists to study it. Grace discovers that astrophages are
single-celled organisms impenetrable to
electromagnetic radiation. The astrophage breeds on Venus, feeding on the planet's carbon dioxide atmosphere and energy from the Sun. The Petrova line is created by astrophage
propulsive emissions as they migrate between the Sun and Venus. Their emissions can be used to construct an incredibly efficient but dangerous spacecraft engine. The astrophages have infected other stars within Earth's
solar neighborhood; Stratt discloses Project
Hail Mary, an international effort to send a crew to
Tau Ceti, the only undimmed nearby star, to investigate. It is a
suicide mission; the
Hail Mary spacecraft can carry only enough astrophage fuel for a one-way trip, but the crew's research will be sent back to Earth via
probes. In the present, as Grace approaches Tau Ceti, an alien spacecraft docks with the
Hail Mary. It is made of solid
xenon, which Grace dubs "xenonite". The ship's pilot is a rock-like, five-legged alien from a planet in the
40 Eridani A system; Grace calls the alien "Rocky". He deduces that Eridians "see" via
echolocation, and creates a
machine translation system to interpret Rocky's
musical chords-like speech. Rocky is a
mechanical engineer and also the sole survivor of a mission to stop the astrophage. Neither can survive in the other's atmosphere, so Rocky enters
Hail Mary using a small, pressurized ball of xenonite as a
spacesuit. Following Tau Ceti's Petrova line, Grace and Rocky discover that the planet
Tau Ceti e, which Grace names "Adrian", harbors an organism ("Taumoeba") that preys on astrophage, controlling their population. After learning that Grace cannot return home, Rocky offers enough astrophage to refuel the
Hail Mary. While gathering the organism from Adrian's upper atmosphere, a fuel leak causes an
uncontrollable spin that renders Grace unconscious. Rocky breaks his spacesuit and saves Grace, but is severely injured. While Rocky recovers in hibernation, Grace learns how to
selectively breed Taumoeba to survive in Venus's atmosphere. Rocky revives, and the two friends depart for their home planets. In a flashback, an astrophage explosion kills the scientist training to travel aboard the
Hail Mary and his backup. With no time to train a replacement, Stratt asks Grace to take his place. When he refuses, Stratt has him
crimped. En route to Earth, Grace discovers that the organisms have evolved to pass through their xenonite containers and are eating
Hail Marys astrophage fuel. Grace repairs the problem on his ship but realizes that Rocky's ship is made entirely of xenonite, which allows the Taumoeba to consume all his fuel, stranding him and dooming his world. Grace chooses to save Rocky and the Eridians rather than return home, sending the Taumoeba and his research to Earth via the probes. Stratt receives the probes, allowing humanity to stop the astrophage. Grace lives in an artificial
biodome on the Eridians' planet. Rocky tells him that Eridian scientists have finished preparing
Hail Mary to return to Earth. Grace considers whether to return to Earth. While contemplating the news, Grace begins another day of teaching science to Eridian children.
Notes ==Cast==