In 1962, the relationship between the USA and the Soviet Union is incredibly tense, and rumors say that the Soviets would drop an atomic bomb soon. Panic takes over American citizens and building bomb shelters in their backyards becomes a common occurrence. Doctor Calvin works extra hard on his bunker, filling it up with enough supplies to last for many years.
One day, Calvin and his pregnant wife Helen throw a party at their house. Things are going well until they see on TV a broadcast from President Kennedy, who announces that they are planning a secret mission against the Soviet Union. There aren’t any details, but Calvin still panics and thinks a war is about to start, so he kicks out all the guests and drags his wife into the bunker.
Seconds later, an aircraft flies over the city only to suddenly detect a mechanical failure. There is nothing the pilot can do and it crashes right into Calvin’s house, absolutely destroying it. In the bunker, Calvin hears the noise and feels all the shaking, so he assumes the war has started and quickly seals the door.
He explains to Helen that he can’t open it manually, the door will open on its own after thirty-five years which is the time for nuclear particles to normalize in the atmosphere. Soon the authorities arrive to check the debris left by the accident and since they can’t find any proof of life, they assume Calvin and Helen have died in the crash. Days start to pass and Calvin feels at home, but Helen hates it down there.
One day her water finally breaks and with the help of her husband, she gives birth to a cute baby boy. Soon days become years, and their son Adam becomes a bright young child. Calvin teaches him everything he knows and hopes that one day Adam will rebuild the country to bring back its old glory.
On top of all the basic school subjects, Calvin also teaches Adam how to box, to speak French and Latin, and how to handle the stock market. Helen teaches him to do chores around their home and even how to dance. Calvin also gifts Adam his collection of baseball cards and tries to explain sports to him, but Adam has some trouble imagining so many people.
Both parents teach them very good manners but never curse around their son, who is growing up to be very naive and sheltered. The family easily finds a routine to suit their daily life that allows them to go pretend-shopping in the mini-mart, fake-fishing in a tank, take care of plants, and build an extra room for Adam. They also have a lounge area to read, play games, and simply relax while hanging out.
Meanwhile above them, the land that used to be their house is sold and becomes a variety of business through the years. First it is a diner, then a pizzeria, and later a nightclub. In 1995, Adam turns thirty-three and gets gifts his parents made themselves.
When he blows the candles he wishes to find the perfect partner one day. Helen mentions there are only two years left and Calvin says he will miss this place when the time comes, causing Helen to go into another room to scream her frustration out. In 1997 the thirty-five years finally end and the door opens itself.
The family is excited to get out, but Calvin tells them he should do a quick check first to make sure it’s safe. After putting on a radiation suit, he takes the elevator out and appears in an abandoned building that has become the home of a bunch of drunk beggars. Melker is so shocked by the vision of a glowing man emerging from the ground that he passes out.
Then Calvin leaves the building, only to be shocked by all the changes. There are graffiti everywhere, people handling guns as if they were toys, adult stores full of merchandising that disgusts him, and weird-looking people who he can’t understand when they speak. Terrified, Calvin rushes back to the bunker and explains that although the air is breathable, the neighborhood is still a post-apocalyptic wasteland full of crazy mutants.
He concludes they must stay in the bunker, and his words cause Helen to finally snap. She yells at him as she explains how sick she is of being locked up and how important it is for Adam to get in contact with nature. Calvin refuses to change his mind and the argument causes him to have a heart attack.
With Calvin sick and supplies almost running out, Helen decides to send Adam outside to get enough food for a couple of years. She gives him some cash and a shopping list, telling him to stay at the Holiday Inn and to keep an eye out for a not-mutated girl. Before Adam leaves, Calvin tells him not to enter the adult video store because it has harmful levels of radiation.
Once he is done packing, Adam finally goes outside and discovers Melker has started a little temple around the elevator to worship Calvin’s family, considering them holy beings. Adam goes outside and is incredibly happy to finally see lots of things for the first time: the amazing sky, buildings, trees, and even other people, who consider him a weirdo. He gets excited over every single little thing and says hello to any person walking by him, accidentally using a slur to refer to a black woman when he greets her because he is extra excited to see another skin color.
When he passes by the adult video store, he covers his nose and warms others to do the same. Afterward he gets on the bus and gets really scared to feel the machine moving. When he tries to talk to other passengers, he uses old words and nobody can understand him, so they also think he is a weirdo.
Eventually Adam makes it to the grocery store and starts picking up all the items from the list. The butcher explains that if he makes a larger order it can be delivered to his house, which makes Adam realize he has no idea how to get back to the bunker. Panicking, he rushes out of the store and spends the day riding different buses to look for the bunker to no avail.
He is also running out of cash, so he enters a hobby shop to sell his father’s baseball cards. The shop owner can tell these are antique and valuable cards but instead of telling Adam, he offers to buy the whole pack for just five hundred dollars. Before Adam can accept, the shop’s assistant Eve interrupts them and tells Adam he is being scammed because each of those cards costs between four and six thousand dollars.
Eve insults her boss and quits on the spot, causing Adam to become very impressed by her and start developing a crush. Once they leave the store, Adam asks Eve to take him to the Holiday Inn. At first Eve refuses and tries to run away from him, but she quickly changes her mind when Adam promises to pay her with two baseball cards.
During the ride, Adam chooses all the old songs on the radio, which Eve finds pretty weird. As soon as Eve drops Adam at the hotel, she leaves without a word. Adam goes to his room and when he looks through the window, he is shocked by the view he has from the eighteenth floor, then he enjoys watching television in color.
He also makes sure to wake up extra early to watch the sunrise. The next morning, Eve visits Adam at the hotel to give him back the cards because she feels guilty over getting paid so much for such a simple task. Then she tries to leave, but Adam stops her with an offer: he will pay her to become his assistant and she can help him gather all the things for the bunker.
Eve agrees and they go shopping together for enough supplies to last two more years, hiring several trucks in the process. Adam also shocks her by revealing he wants to find a wife. After they’re done shopping, Even takes Adam to her house and he meets her roommate Troy, who starts asking Adam tons of questions when he notices how surprised he is by all the technology.
Adam lies, saying he is from Alaska and that he is here for a business trip. Meanwhile Helen is too curious and gets on the elevator, but as soon as she comes out, she sees Melker and his friends being creepy and immediately goes back. The next day Troy decides Adam needs a fashion makeover, so he gives him a whole new wardrobe that makes him look even more handsome.
The next few days, Eve and Troy take Adam on many new experiences, like dancing to modern music, skateboarding, and seeing the ocean. Adam gets so excited that he jumps right into the water without a care. He also gets to watch a baseball game and finally understands why his father likes it so much.
One afternoon it starts raining and Adam stands under it in pure awe. When Eve comes to check on him, Adam hugs her to share his joy, saying his father would call this a miracle. In the evening, Eve and Troy take Adam to an old-school swing club to find him a wife and they tell him just to be himself.
Women in the club immediately get attracted to Adam’s sweet personality, respectful manners, and handsome looks. Eve’s rival quickly gets his attention and they start getting along, which makes Eve jealous. She drags Adam to the side and tells him that she needs a sweet woman in his life, not a skank.
Afterward Adam asks another girl to dance and they take over the dance floor, impressing everyone with his amazing dancing skills. Eve tries to ignore her jealousy and chats with her ex-boyfriend, who makes fun of Adam and taunts him into a fight. However Adam uses his boxing lessons to quickly scare the guy away.
Irritated by all the drama, Eve leaves the club and goes home alone. When Troy arrives, he informs her that Adam left the club with her rival, causing Eve to realize she loves Adam and rush out to find him. She gets in the car but before she can take off, she is startled by someone knocking on the window and falls on the ground.
It’s Adam, who takes her inside and takes care of her scratch while explaining he had to reject the other girls because he couldn’t stop thinking about Eve. Adam confesses his feelings for Eve and they finally kiss. Now that they are together, Adam decides to finally tell Eve the truth about his family and his home, adding the fact he wants to marry Eve so she can live with him in the bunker.
However Eve thinks he is actually a crazy man who has been good at hiding it and immediately kicks him out. The next day, Troy takes Adam around town while teaching him how to drive. Suddenly Adam sees the adult video store from before and follows the road to finally find the building above his bunker, where Melker has started a whole religion around the elevator.
Excited, he rushes back to Eve to give her the news, only to find two psychiatrists waiting for him. At first Adam pretends to cooperate but as soon as he sees an opening, he runs away. While a doctor chases after him, the other tries to call the police, but Eve stops her and realizes that what she did was wrong.
At that moment Adam runs near her and gives her his hotel key so she can pay the bill with the cards, then he escapes in the truck he’s rented, accidentally hitting the doctor’s car in the process. Later Eve and Troy make it to Adam’s hotel room and find a bunch of items that were made in the sixties, not to mention Calvin’s stock certificates that are now worth millions of dollars. These things make them realize Adam told them the truth.
Meanwhile Adam finally returns to the bunker and hugs his parents after two weeks of not seeing them. He tells them the outside world is lovely and brings in the supplies, which are being loaded by Melker and his friends. Back to Eve, she is desperate to find Adam so Troy takes her to the adult video store and they start stomping on the floor, thinking they may find the bunker there.
Obviously they find nothing and decide to leave, but on their way out, they see Adam about to enter the neighboring building. Eve immediately rushes to him to kiss him and hug him, and Adam invites her to meet his parents. Calvin and Helen like Eve very much and they have dinner together, Calvin also gives Adam a talk about the birds and the bees.
However before making any plans for a new life, Adam asks his parents to wait two months. During the following weeks, Adam and Eve sell Calvin’s stocks and build a new home in the country that looks identical to Adam’s previous house. Melker also helps after cleaning up and finally abandoning drinking.
Once everything is ready, Adam brings his parents to the house, revealing this way they can get used to the new world little by little. Later while Helen and Eve prepare dinner, Adam finally tells Calvin that there was never an atomic war, that the “bomb” had actually been a plane that crashed into their house, and that the Soviet Union collapsed. Calvin refuses to believe it and starts making plans to build a new bunker just in case.