I think the best starting place for this movie is a scene that took place near the end.
Jack Harper (Tom Cruise) and a crew of six others embark on a mission to explore some massive craft in space that orbits earth. As Jack and his crew get closer, the gravity of the massive craft is so strong that it pulls them in and they cannot escape from it. Realizing this, Jack makes a last-ditch effort to disengage a portion of the ship that contains five of the seven crew members. Jack succeeds and the portion containing the five crew members floats freely into space while Jack and his commanding partner board the massive craft. The five crew members are completely unaware of all this because for some reason they are in a sort of hibernation state.
So the portion of the ship containing Jack and his commanding partner drifts into the giant object in space (known as the Tet). Once in the Tet, it is presumed that Jack and his commanding partner are killed and cloned – perhaps not in that order. The details of this and the following series of events are not exactly clear forcing us to infer these parts of the story.
The Tet unleashes havoc on earth by destroying the moon. This disrupts the tidal and tectonic balance causing massive earthquakes and tsunamis. The process decimates nearly everyone and everything. The reason the Tet did this was because it needs energy from planets like earth similar to Unicron from Transformers or Galactus from Silver Surfer. But instead of eating the planet, it sent thousands of Jack Harper clones to earth to set up giant machines that extract energy from the oceans. It also deployed drones to protect Jack Harper and these machines. The drones are also tasked with scouring the surface of earth for any remaining humans that may thwart the Tet’s plan, and are programmed to kill them on site.
The movie starts with Jack Harper (Technician 49) and his female partner – who we eventually discover are clones of the original Jack Harper and commanding officer from 60 years ago. They have no idea they are clones because their ‘memories’ have been wiped clean. They are assigned the thankless mission of staying on earth and repairing any drones if and when necessary. They live in an über-modern house in the sky and are romantically involved.
Jack’s partner acts as his ‘eyes in the sky’ keeping him safe while he is on the surface performing his daily duties. The partner communicates with the Tet, who appears under the guise of a benevolent woman on a video screen. The Tet gives them instructions and protocols to follow, approves or denies requests, and reinforces the promise of one day returning to the Tet. They are told that once they complete their mission, they will be reunited with the other remaining humans from earth who are on board the Tet, and together they will travel to one of the moons of Saturn to establish a new colony.
Each day, Jack goes down to search and repair drones and is told to stay out of certain radiation zones. Jack tries on multiple attempts to persuade his partner to join him on the earth’s surface, but every time she vehemently declines because it is against protocol.
While repairing the drones, Jack gathers items that are left over from the past, such as books, baseballs, and records. Jack must also be on the lookout for ‘Scavs’ – scavengers who he is led to believe are the remaining aliens that destroyed earth. These Scavs watch Jack and notice that he is different than the other clones because he shows an unprecedented curiosity with these lost and forgotten objects from times past.
One day, the Scavs jury-rig some sort of device to a tower and attract the original Jack’s aforementioned disengaged crew, who have been drifting through space in a sleep-like state for the past 60 years. Once the crew ship lands, everyone is killed by drones except one – the original Jack’s wife Julia, who was one of the crew members. Jack rescues Julia, but has no idea who she is. He experiences flashbacks of her – remnants of his original self’s memories. These vague recollections grow stronger after Jack spends the day with Julia. She informs Jack that she is in fact his wife.
Julia convinces Jack to go back to the crash site to retrieve the flight log from her ship so she’ll have a better understanding of what happened. During this operation, the Scavs capture Jack and Julia. They reveal themselves as humans (not aliens) and tell him the truth. The truth is that the Tet is not a ship filled with humans, but rather some artificial intelligence hell-bent on destroying the world for its own sake. Apparently, it needs the energy from planets like earth to keep it alive. Information like who built the Tet, where it comes from, and how it uses the earth as an energy source are never explained.
Together, Jack and Julia enter the forbidden radiation zone. Jack discovers another clone of himself (Technician 52), which confuses the hell out of them both. They fight, and Tech 49 Jack chokes Tech 52 unconscious with a sweet triangle choke. Jack 49 takes Jack 52’s ship, goes back to 52’s house, and discovers another commanding officer, who is a spitting image of his commanding partner. I skipped the part where Jack 49’s commanding partner gets killed and also that she told the Tet that Jack found a woman who had crash landed to earth. So Jack 49 asks Jack 52’s partner if she wants to visit the surface with him and she vehemently tells him no – implying that 52 is much like 49 in that they share the same curious nature that was observed by the Scavs.
Meanwhile, back at the Scav hideout, three drones attack the Scavs. A big fight ensues and the drones eventually get defeated, but not without killing several Scavs. Jack 49 partners with the Scavs and together they devise a plan to destroy the Tet. The plan is to board the Tet and detonate a bomb akin to Luke Skywalker blowing up the Death Star. But before Jack 49 boards the Tet, he leaves Julia behind at a little house he had built by a lake. The house is filled with all the old relics that he had gathered (books, baseball, records…).
So apparently Julia was pregnant with Jack 49’s baby and lived at the house for the next three or four years. We are led to believe she had the baby by herself (now 3 or 4-years old) and fended for the two until one day, Jack 52 and the Scavs find her. It is a big happy moment because Jack 52 has been searching for her for the past three or four years. Since he shares most (if not all) of Jack 49’s memories, he is a sufficient substitute for Jack 49 (who died in the explosion on the Tet) and the original Jack (who also died on the Tet).
My overall opinion of the movie is that it was really good. It started off slow, but that made it suspenseful. While the action and dialogue was limited, it was visually stunning and made for a great sci-fi adventure tale.