Some time in the late 21st century, Earth’s food supply is running out. Crops are going extinct, and dust storms occur with alarming frequency. The government has done away with the military, and schools use standardized testing to determine whether a child will go down one of two paths: to college, or to work as farmers to fight food scarcity.
Cooper, our protagonist, is a widower and former NASA pilot whose wife died of a brain cyst that was not found because MRI machines are no longer made (in order to cut down on the “wastefulness” of the 20th century). He's now a farmer with two kids, Tom and Murphy (referred to throughout the film as Murph). They live together with the kids’ maternal grandfather, Donald.
Murph has been visited by what she calls a “ghost” in her bedroom. Books have been falling off her shelf and she believes the ghost is speaking to her. Cooper tells her that ghosts aren’t real and that she must use science to figure out what is actually happening. Soon after, a sandstorm sweeps through their farm and through Murph’s open bedroom window, leaving Cooper to ponder what is left behind: binary code spelled out by the dust on the floor as it meets a strange gravitational anomaly. Cooper translates the binary code to reveal a set of coordinates. He sets off in his truck to find out where they lead, and Murph stows away with him. They arrive at an unmarked gated facility where they're greeted by a hostile military robot named TARS who knocks Cooper unconscious. Cooper wakes up to find that he and Murph are in a top-secret NASA facility led by Professor John Brand and his daughter, Dr. Amelia Brand. They also meet Doyle and Romilly, two astronauts within the space program. After refusing the government’s order to drop bombs on innocent civilians as a means of population control, NASA has been reinstated in secret, as public opinion is that space exploration during such times of food scarcity is a waste of money.
NASA has found a wormhole near Saturn, placed there by an unknown species referred to as "they" or "them," that allows spacecraft to travel to faraway galaxies containing potential habitable new worlds for the human race. The Lazarus missions have already been sent into the wormhole ten years prior to land on each planet and collect data. The next phase of the mission is to go back through the wormhole and find out which planets are habitable so that they might fulfill one or both of Professor Brand’s plans for saving humanity: Plan A is to solve a difficult gravitational equation and use it to transport humans off the earth by means of a massive space station that will take them to their new planet. If he fails to solve said equation, Plan B is to leave the current Earth population behind and colonize the new planet with embryos in cryostasis. Professor Brand believes that Cooper was chosen by the unknown species to embark on the next leg of these missions since they placed the gravitational anomaly in his home, just as they placed the wormhole in space.
Cooper decides to go. Heartbroken, Murph tries to convince him to stay, saying she's decrypted the message her "ghost" left her using the books that fell off her bookshelf, and that it says “STAY” in Morse code. He gifts her a watch to remember him by and leaves anyway, promising that he will return but knowing that in fact he may not. Murph is devastated.
Cooper, Dr. Amelia Brand, Romilly, Doyle, and the two military robots CASE and TARS begin their nearly two-year journey on the space station Endurance towards the wormhole. After traveling through it, they are able to collect the data from the Lazarus missions to determine which planet they should navigate toward. There are three astronauts—Miller, Edmunds, and Mann—on three separate planets. They choose Miller’s planet, the closest of the three, which orbits a massive black hole named Gargantua. A single hour on the planet equals more than seven years on the space station (and back on Earth) due to Gargantua's huge gravitational pull. Romilly decides to stay behind on the Endurance to study the black hole while Cooper, Brand, and Doyle visit the planet in a smaller craft. While on it, they encounter enormous tidal waves that kill Doyle and waterlog their ship's engines. Cooper and Brand are stranded for hours until the engines can drain. When they return to the Endurance, Romilly has been waiting for them alone for 23 years.
Cooper watches years of messages from Tom, now a grown man with a wife and child. Tom says he's decided to make peace with the fact that his father is gone. Donald has passed away, as has Tom's first son, Jesse. Murph leaves Cooper a single message once she turns the same age that he was when he left. Murph has become a scientist working with Professor Brand at NASA to solve the gravitational equation that will allow humanity to leave earth via Plan A. They haven’t solved it yet, but Murph has faith that they will.
Back on the Endurance, Cooper, Brand and Romilly no longer have the fuel to check both of the remaining planets and must pick one. They choose Mann’s planet because his beacon is turned on, signaling that the planet is habitable, and because they believe the brave Dr. Mann represents “the best of us.” Dr. Brand protests, saying that Edmunds’ data is promising. Cooper deduces that she's in love with Edmunds and dismisses her, but she argues that love is a powerful force that they should consider as a factor in their decisions. Cooper disagrees and sets course for Mann's planet.
On Earth, Professor Brand admits on his deathbed that the equation he was seeking to solve was a red herring used to distract Cooper, Murph, and everyone else from trying to save the people on earth. NASA's mission was always to colonize the new planet via Plan B, using the embryos in cryostasis, leaving the people on earth behind to die. Murph is horrorstruck and sends a message to Dr. Brand, asking if she knew the truth.
Cooper, Brand and Romilly land on Mann’s cold, barren planet and awaken him from a deep sleep. As Mann is telling them about the planet's habitability, they receive Murph's message that Plan A was a lie. Everyone is shocked except Mann, who says he knew it to be true all along. Cooper decides to return to Earth.
While briefly exploring the planet together, Dr. Mann attempts to kill Cooper, cracking his helmet and leaving him to suffocate. He reveals that he faked all his data and that the planet was never a viable option for life. He admits that he turned on his beacon only because he wanted to be rescued. Romilly is killed by a booby trap as Mann steals one of their spaceships and heads for the Endurance. Brand is able to rescue Cooper with another spaceship and she, Cooper, TARS and CASE chase after Mann, who has turned off his radio communication. TARS disengages Mann's ship's autopilot so that he'll have to dock with the Endurance manually. He does so, but improperly, preventing the airlock from engaging. When he attempts to open the hatch to get inside, he blows a hole in the Endurance, killing himself and sending the station into a death spiral toward the planet. Cooper, with the help of TARS and CASE, is able to dock their ship with the Endurance and stop its spinning, but they are now in the gravitational pull of the black hole, Gargantua, and are unable to navigate out of it.
Cooper decides to use gravity and the thrust from the remaining ships on the space station to slingshot them around Gargantua and on toward the third planet where Edmunds is. They will send TARS into Gargantua to collect data and attempt to send it back to Earth to help Murph solve the gravity equation. After TARS detaches, Cooper shocks Brand by detaching as well, sacrificing himself to shed the weight and sending her on to Edmunds' planet alone. He descends into the black hole and has to eject. Falling through space, he finally comes to a halt inside a strange, three-dimensional space where he can see every instance of time that has occurred in Murph’s bedroom. TARS begins to communicate with Cooper from another point in space, saying that “they” are five-dimensional beings who have left behind a three-dimensional space to help Cooper experience time as a place. Cooper has quite literally become the ghost inside Murph's bookshelf. With this information, Cooper uses gravity and his love for Murph to leave behind clues for her, including the Morse code in the bookshelf that says, “STAY.”. He manipulates gravity to send his past self the binary coordinates for NASA, and also places the quantum data necessary to solve the gravity equation as Morse code ticking on the hands of the watch he left with Murph as a child.
Back on Earth, the fully grown Murph finds the watch transmitting the data via Morse code in her childhood bedroom. When she does, the three-dimensional space that Cooper is in begins to collapse and he wakes up in a hospital room aboard Cooper Station, named for Murph and currently orbiting Saturn. Murph succeeded in using the data Cooper sent on the watch to save the people of Earth.
Cooper reunites with his daughter, who is now an old woman near the end of her life. Murph tells him to go and find Brand, that she has her kids to take care of her now. As Cooper commandeers a space ship, we see that Brand has found Edmunds’ planet. Edmunds is dead, but the planet has a breathable atmosphere and she has set up camp in order to be found.
