Lee min-ho and Hyun Bin both are decided to make a Time machine. Because , While leaving on a train, Lee min - ho's father dies in an accident and other side,while Hyun Bin's father and Kim Bum are absent, he is asked to look after his mother, who has a heart condition. However, he goes out on a date with Kim Ji-won. He gets continuous phone calls from his mother, which he ignores despite Kim Ji-won insistence to pick them up. However, on returning home, he finds out that his mother had died of a heart attack.
Lee min-ho and Hyun Bin wants to go particular date with the help of time machine to save there parents.
Firstly, They want to save Lee min-ho's father Simon.
On 28 March 1998, scientists Paul and Michael carry out an experiment on their time machine, however, the machine fails and Michael dies in the process.
One day, Paul calls Rutherford, who is a real estate agent, to find him in a house on the outskirts. Rutherford takes Lee min-ho and Hyun bin along to show Paul the house. However, Lee min-ho is surprised to see the boxes dated 28-03-1998 which was a day before his Father died. Paul overhears this and convinces Lee min-ho that he can save his father using the time machine, in return, Lee min-ho must save Michael from death by stopping the experiment. Hyun Bin and Rutherford tag along to change their own fate. They place the time machine in the abandoned house of Rutherford's grandfather. Paul explains to them the rules of time travel. The date is set to 1 March 1998 and the three travel back in time. They see their younger selves in their school and disguise themselves to get close to them. Lee min-ho befriends his Father and joins as the guitar teacher to his younger self, nicknamed Kutlu. Lee min-ho tries to make sure that his Father is safe who is set to die in a Train accident. Rutherford becomes an Taxi driver to bring his younger self close to Lilly who grows up to be a beautiful woman while Hyun Bin joins as a peon to personally oversee his younger self's education.
Kutlu prepares to participate in his school's cultural competition on 26 March 1998. Lee min-ho's Father drops Kutlu at his school that morning. he gives him his ring to be confident during his performance. However, young Hyun Bin and Rutherford suspect and follow their older selves, and find the time machine. They inform Kutlu about this and the three leave the school without any intimation. The time machine turns on upon scanning Kutlu's iris (which is the same as Lee min-ho's). The machine brings the kids to the future in 2023. The older three realize their younger selves are missing along with the time machine which also contains the details of Paul of 1998. They realize that the only way to set things right is to find Paul and use his old time machine to travel to 2023.
Meanwhile, the police file a kidnapping case to find the missing kids and treat older Hyun Bin and Ruther ford as suspects. Lee min-ho's Father goes into a depression, therefore, Lee min-ho promises her to bring back her son. The older three try to find Paul, only in vain. Upon realizing that they arrived in future, the younger three aimlessly roam the city to seek help until Lee min-ho's girlfriend Song hye-kyo finds them. She is shocked to realize they are younger Lee min-ho, Hyun Bin and Rutherford. Paul explains everything to Song hye-kyo and says that he needs a day to reset the time machine to send the kids back. Kutlu overhears that his father is going to die. The three escape and learn the truth.
On 28 March 1998, the older three accidentally come across Michael but are chased by the police. They find the old time machine and plead with Paul to turn it off. Michael goes ahead anyway and dies in the accident. The police take everyone into custody but Lee min-ho escapes the following day to save his Father. Lee min-ho finds his father on the Train . He tries to convince him to get back to safety but as he refuses, Lee Min-ho confesses that he is his son. However, Lee min-ho's Father dies after he leaving on a train.
The older three contemplate that it is pointless to try changing the past. Lee min-ho is content that he is able to spend time with his Father again. Meanwhile, Paul sends the kids back in time. The older three advise the younger three to be themselves and enjoy every moment in life. The older three restart their lives in present with new vigour.
After the failure of the Time Travel. Hyun Bin decided to go himself to the particular date to save his mother.
Prof. Einstein a scientist strives hard with enormous experiments and invents a time machine that travels in time. the daughter of Prof. Einstein. Jennifer considers her father's experiment futile. When Hyun Bin visits their house, Einstein presents his time machine but it breaks down.
One night, Adam secretly visits Prof. Einstein's residence joins the remaining children in the hospital and starts the time machine. Being cognizant of it, Hyun Bin and Jennifer rescue them but get struck and it takes off. Parallelly, as an anecdote, a police constable hunting a thief is also trapped in the machine.
As of today, they land in 2504, a dystopian world destroyed by radiation after the end of the Third World War. Scientists of that era who already know about their arrival, receive them. In this era, the entire city is built underground where finds several wonders in the future.
However, a risk is lurking for them as they can live in that time only for 8 hours in this climate and also watch the news from the year 2023.The malfunctioning time machine is now repaired and when the environment begins to negatively affect them, they leave and back to the present. At last, Hyun Bin backs safely by jumping off the cliff moments before it explodes when it is revealed that they fail to get complete information in the future.