The crew of the Space Shuttle Explorer is working on the STS-157 mission. Mission Commander Matt Kowalski, medical engineer Dr. Ryan Stone - who is on her first ever space mission - and flight engineer Shariff Dasari are on a space walk when they learn from Houston control that an explosion has just occurred at a Russian satellite. Before the crew can do anything about it, the explosion debris comes hurtling toward Explorer, irreparably damaging the shuttle and station, immediately killing all the crew except Kowalski and Stone, and knocking out at least incoming communication with Houston control, although they have no idea if there is outgoing communication. The two are left in a precarious position as Stone is untethered with quickly decreasing oxygen on her person meaning that Kowalski has to retrieve her quickly if she has any chance of survival. Even if he can retrieve her and get her some oxygen, they have the difficult task of trying to get to another satellite with whatever equipment is on hand, and from there ultimately back to Earth. Through the process, they are often on their own without the other leading to an extreme feeling of isolation which leads to individual questions and ultimate decisions about their own mortality and what may be best for the other at the expense of oneself.