When a malfunction occurs aboard the luxury space cruise ship Avenue 5, it's up to engineer Billie McEvoy to warn Capt. Ryan Clark, owner Herman Judd and his right-hand woman Iris Kimura that the incident may have a cataclysmic knock-on effect.

While Karen oversees an effort to jettison non-essential passenger items, Billie tries to teach an inattentive Ryan how to dock the ship. Matt learns of Judd’s plan to make the “ultimate sacrifice” by returning to Earth. Meanwhile, the passengers suspect all is not as it seems with the journey.