Dr. Ryland Grace wakes aboard the Hail Mary with total amnesia, connected to an IV and tended by robotic arms.

A pendulum experiment confirms that gravity aboard the ship is 1.5G, proving Grace is not on Earth.

In flashback, a friend named Marissa tells Grace that the sun is dimming at the same rate the Petrova Line grows brighter.

A mission leader named Stratt visits Grace's classroom and recruits him to examine extraterrestrial samples from the ArcLight probe.

Grace examines the ArcLight samples, determines the black dots consume stellar energy, and names the life form Astrophage.

Grace discovers four Beetle probes aboard the ship and calculates there is not enough fuel for a return trip to Earth.

Grace activates the Petrovascope and discovers an alien spaceship hovering within a few hundred meters of the Hail Mary.

Grace signals the alien ship with engine flashes and receives a signal back, confirming there is intelligent life aboard.

Grace opens a xenonite cylinder from the alien ship and finds a scale model identifying the visitors as being from 40 Eridani.

A spider-like alien, later named Rocky, is revealed through a transparent tunnel divider, and the two wave to each other.

Using their developing shared vocabulary, Grace and Rocky confirm that both their home stars are infected with Astrophage.

Grace and Rocky discover Taumoeba, a natural Astrophage predator, in a sample collected from the planet Adrian's atmosphere.

In flashback, an Astrophage explosion kills DuBois and Shapiro, and Stratt drugs Grace and forces him onto the Hail Mary.

Grace launches the Beetle probes and turns back toward the powerless Blip-A, choosing to rescue Rocky instead of returning to Earth.

Rocky visits Grace on Erid to share that scientists have confirmed Sol has returned to full brightness, meaning Earth was saved.

Dr. Ryland Grace wakes aboard the Hail Mary with no memory, slowly piecing together that he is on an interstellar mission to save Earth from a star-consuming alien life form called Astrophage. As his memory returns through flashbacks, he recalls being recruited by the ruthless mission leader Stratt and ultimately being drugged and forced onto the one-way trip after his original crewmates died. In the present, Grace discovers he is in another solar system and makes contact with an alien spaceship, eventually befriending a spider-like Eridian named Rocky who is on the same mission for his own species. Together, Grace and Rocky discover Taumoeba, a natural Astrophage predator, and race to breed a strain that can save both their home worlds. In the novel's most pivotal choice, Grace abandons his return journey to rescue a stranded Rocky, sacrificing himself for his alien friend. The story ends with Grace living on Erid and receiving the news that Earth's sun has fully recovered, confirming that Project Hail Mary succeeded.

The central mission: from amnesia to saving humanity.

Grace finds the desiccated corpses of two crewmates in the dormitory beds and concludes only he survived the coma.

Grace builds a makeshift pendulum and calculates he cannot be on Earth, on another planet, or inside any reasonable centrifuge.

Grace recalls his own name while reviewing a NASA livestream memory and uses it to unlock the hatch to the control room.

In flashback, Grace accidentally breeds Astrophage and maps their full life cycle, including migration to Venus to reproduce in carbon dioxide.

Scientists on the aircraft carrier reveal that every nearby star except Tau Ceti is infected with Astrophage, motivating the Hail Mary mission.

In flashback, Dr. Lokken proposes transforming the Hail Mary into a giant spinning centrifuge to create Earth gravity for existing lab equipment.

The Hail Mary transforms into centrifuge mode and the alien Blip-A mirrors the maneuver, creating the first interspecies miscommunication.

The Blip-A attaches a divided xenonite tunnel to the Hail Mary's airlock, creating a safe meeting space between incompatible atmospheres.

Rocky moves into the Hail Mary with xenonite-making supplies so that he and Grace can work together directly on solving the Astrophage problem.

Rocky engineers a 10-kilometer xenonite chain to collect Astrophage samples from deep within the planet Adrian's atmosphere.

Rocky exits his pressurized compartment and rescues an unconscious Grace from the control room, exposing himself to Earth's oxygen atmosphere.

Grace returns Rocky to his pressurized compartment to save Rocky from Earth's oxygen and suffers severe chemical burns from ammonia exposure.

Taumoeba infest the Hail Mary's fuel lines during a total blackout, leaving Grace without power or propulsion.

Grace successfully breeds Taumoeba-82.5, which can survive the 8% nitrogen concentration found in the atmosphere of Rocky's home planet.

Grace is established on Erid, surviving on Eridian-made vitamin shakes and lab-grown protein after choosing to sacrifice his return to Earth.

This pool traces the scientific and engineering breakthroughs that define the Hail Mary mission, from Grace's earliest investigations aboard the ship to the discoveries that ultimately save two civilizations. In flashback, Grace maps the Astrophage life cycle, learns that Tau Ceti is uniquely uninfected, and collaborates with scientists like Dr. Lokken to design a ship capable of sustained scientific work in deep space. In the present, Grace and Rocky establish the physical means of collaboration through the xenonite tunnel and centrifuge maneuvers, before Rocky moves aboard and the two undertake increasingly dangerous experiments, including deploying a 10-kilometer xenonite chain to fish for samples from deep inside an alien atmosphere. Their risky collection mission nearly kills both of them, but their sacrifice allows them to identify and breed Taumoeba as a solution for both worlds. After a catastrophic blackout caused by a Taumoeba infestation of the ship's fuel lines, Grace engineers a workaround using the Beetle probes, and the pool closes with Grace established on Erid, having chosen to sacrifice his return home to ensure Rocky's survival.

The science and engineering milestones behind the mission.

The ArcLight probe returns images of black microbe-like dots moving along the Petrova Line, suggesting an extraterrestrial life form.

In flashback, Grace discovers that a punctured Astrophage cell is mostly water yet maintains a constant internal temperature of 96.41 degrees Celsius.

In flashback, Stratt asks Grace to confirm that only astronauts with a coma-resistance DNA marker should be selected as Hail Mary crew.

Imprisoned engineer Robert Redell designs a blackpanel solar farm covering a quarter of the Sahara to breed and energize Astrophage fuel.

Nuclear weapons are detonated to break Antarctic ice into the sea, intentionally triggering global warming to slow Earth's cooling from the dimming sun.

Grace spacewalks to retrieve the xenonite cylinder sent from the alien ship and discovers it is scalding hot despite traveling through cold space.

Grace and Rocky establish a shared vocabulary and numerical system by exchanging analog clocks and using soundwave-analyzing software.

Rocky reveals to Grace that he is the only surviving member of the Blip-A's original 23-member Eridian crew.

Grace admits to Rocky that the Hail Mary is a suicide mission, and Rocky offers his surplus Astrophage as fuel for Grace's return trip.

Grace realizes Eridians have no concept of relativity, which is why Rocky unknowingly arrived at Tau Ceti faster than expected with excess fuel.

Grace repurposes the four Beetle probes as substitute hull thrusters to restore movement to the powerless Hail Mary after the blackout.

In flashback, Stratt confronts Grace in his cell, calls him a coward, and reveals her plan to use a French amnesia drug to force him aboard.

Grace determines that nitrogen kills Taumoeba and begins breeding a nitrogen-resistant strain capable of surviving on Venus and Rocky's home planet.

Grace discovers that Taumoeba-82.5 has evolved to burrow through xenonite, meaning Rocky's Astrophage fuel tanks are in deadly danger.

Grace settles into life on Erid, teaching science to young Eridians using the same lightning-round quiz style from his old classroom.

This pool highlights the key revelations and pivotal decisions that fundamentally reshape the course of the mission. From the earliest identification of Astrophage as a possible alien life form to the escalating moral dilemmas of Project Hail Mary's preparation—including bombing Antarctica and building a Saharan fuel farm—the stakes are established through a series of uncomfortable choices made by Stratt and her team. The first contact with Rocky unfolds through careful communication breakthroughs, while turning points like Rocky's revelation that he is the last Eridian survivor and Grace's confession of his suicide mission deepen their bond and shift the mission's emotional core. Grace's discovery that Eridians lack any concept of relativity unlocks a lifesaving solution to his fuel problem, while the late revelation of Stratt's amnesia drug finally explains the mystery of Grace's missing memories. The pool closes with Grace discovering that Taumoeba can burrow through xenonite—endangering Rocky's ship—and ultimately settling on Erid as a teacher, having completed his arc from reluctant draftee to selfless hero.