In a flashback, Ryland meets a coma tech expert who confirms that only certain individuals with coma-resistant genes have a chance at survival. Eva Stratt insists that everyone involved be tested for these genes, including herself and Ryland. Though Stratt never tells him, Ryland is confirmed to be a match.
On the Hail Mary, Rocky and Ryland now begin doing science together to figure out how to save their planets. Rocky enters the Hail Mary in a geodesic ball with a life support system. In the first of many discussions about time, Rocky tells Ryland he has been alone in the system for 46 Earth years, and that his planet faces a more gradual decline than Earth, even accounting Eridians longer lifespans. For his part, Rocky discovers that time passes differently under relativistic speed, explaining previous mysteries about why he has additional fuel in his storage. Bittersweetly, this means he has plenty of Astrophage fuel to offer Ryland hope of escaping his suicide mission.
Rocky begins constructing xenonite chambers in the Hail Mary so that the two can continue deeper experiments and save both planets.
In a flashback, Stratt assembles a crew with coma resistant gene markers, along with backup crews and strictly mandates separation for the primary and backup crew. In addition to this, she has a wide range of criteria that strikes Ryland as sexist and racist. Ryland, now the world expert on astrophage, is assigned to train the crew on astrophage biology.
Back on the Hail Mary, Rocky and Ryland set their sights on the Astrophage home planet in the Tau Ceti starsystem, which they name Adrian after Rocky’s mate
Upon falling into Adrian’s orbit, Ryland performs an EVA to collect samples. The planet’s methane rich atmosphere suggests the potential for biological activity. Evaluation of the samples reveals a diverse ecosystem which leads to a potential lightbulb hypothesis: If astrophage has a predator, that could rescue the afflicted planets. The renewed sense of hope leads Ryland to teach Rocky a celebratory fist
A flashback reveals Ryland’s training in NASA’s and there is some oversharing of personal dynamics by crew members, where they disclose that the primary and backup crew mates are in a relationship, knowing that in a few months, one of them will travel to their deaths. Back on the Hail Mary, Although Ryland and Rocky fell into Adrian’s orbit, the outer atmosphere where it is safe to venture, yields nothing and they need to build a collection device and a chain link from scratch and then Ryland must retrieve this under extreme conditions.
Their efforts pay off, but upon re-entry, the ship suffers damage that throws it into a spin. Ryland is nearly killed by the g-forces, but Rocky risks his life to save Ryland by entering his environment.
Ryland in turn hauls Rocky back to the safety of his own environment and suffers considerable injuries in the process. Ryland regains consciousness first and works on a solution to stabilize the sample he has retrieved and clear Rocky’s system of the damage sustained by his exposure to oxygen. The treatment works—or so he thinks. When Rocky wakes up, he tells Ryland that he actually interfered with his healing process.
In a flashback, crew members discuss their preferred methods for elective death at the end of the mission. Days before launch, a tragic accident kills both carefully selected primary and the backup crew member.
On the ship, Ryland studies the sample retrieved from Adrain and discovers the amoeba that is voraciously consuming astrophage and names it taumeba.
Ryland loses power to his ship, and discovers that Taumoeba has infiltrated the Hail Mary’s fuel tanks, rendering the ship inoperable. Rocky’s systems are still functional, so they formulate a plan: use the uncontaminated Beetle return probes aboard the Hail Mary to travel back to Blip-A, Rocky’s ship, where more Astrophage fuel can be collected.