It's the near future and the sun is dying, thus meaning nuclear winter has enveloped Earth and is threatening the future of humankind. Following the failure of a similar mission seven years earlier, the crew of the Icarus II is now en route toward the sun with hopes of jump-starting its faulty fusion-based core, thanks to a device devised by physicist Capa (CILLIAN MURPHY).
Even at a distance of 36 million miles, the ship is so close that it would burn up without the protection of its solar shields, a point not lost on psychologist Searle (CLIFF CURTIS) who's fixated on all things sun related. That is, when not having to deal with petty, testosterone based skirmishes among the crewmembers, such as between Capa and communications officer Harvey (TROY GARITY) or engineer Mace (CHRIS EVANS).
Of course, that doesn't apply to pilot Cassie (ROSE BYRNE) or botanist Corazon (MICHELLE YEOH) the latter who cares for the ship's life-giving oxygen farm, while Captain Kaneda (HIROYUKI SANADA) is fixated on the failure of the first mission that was led by Captain Pinbacker (MARK STRONG).
Kaneda gets the chance to explore that further when Harvey reports that they've picked up the distress signal from the long-lost Icarus I. After much discussion about whether to rendezvous with the ill-fated ship, navigator Trey (BENNY WONG) sets course for it. Yet, a miscalculation on his part leads to an unexpected disaster.
From that point on, the captain and his crew must decide how to proceed, all while dealing with unexpected complications as well as their driving desire and need to accomplish their task, lest everyone back on Earth perish.