On Christmas Day 2004 near Indonesia, a fishing boat is hit by a severe storm.
On land, a weather center detects anomalies that indicate the onset of a tsunami, so they
rush to the boat's rescue.
The helicopter has only five minutes to get the crew before they are crushed by the big
wave, and although everything seems to go relatively smoothly, Mr. Kang, one of the
members, is trapped under some boxes, preventing him from getting out.
His friend Man-Sik tries to help him with all his might, but his attempts have no effect,
so he’s rescued and watches his friend succumb to the weight and force of nature.
A couple of days later, the tsunami event caused a national impact, with damages in
places like India, Indonesia, and Sri Lanka, leaving thousands dead and injured.
Five years later in the summer, Man-Sik is trying to pull out a loose tooth of his son
Seung-hyun on the beach, but then a friend appears and tells him that he must leave with
him immediately.
On the street, the owner of a seafood store complains to a girl for selling fish in front
of her stall, accusing her that her attitude stems from being an orphan.
The conflict escalates to blows, but they are promptly separated by Man-Sik, who reveals
himself to be the lady's son and the head of the Prosperity Association.
He overly protects this girl for being Yeon-hee, the daughter of his former shipmate, whom
he swore to take care of.
While he has a high regard for Yeon-hee, she assures him that she doesn’t need his protection.
At that moment, a group of investors appears together with Eok-jo, a businessman who assures
that Haeundae is a tourist site suitable for investment, but just at that moment he is
assaulted by one of the citizens, who criticizes him for taking advantage of the town's situation
to become richer.
Meanwhile, geologist Kim Hwi warns a board of investigation about the dangers of a possible
new tsunami.
Kim Hwi's personal life takes a toll on him as he is in the middle of a divorce with his
wife Yoo-jin.
Outside the meeting, Kim Hwi is surprised by Ji-min, his daughter with Yoo-jin, but
who is unaware of their relationship, and who remains part of the woman's new family.
Back on the beach, three girls are surprised by three boys, who take them on a yacht out
to sea.
One of them, Hee-mi, doesn't look so impressed, but the others ask her to go with the flow
to take advantage of this opportunity.
Parallel to this, local bum Dong-choon and Seung-hyun plan a scam where he pretends to
be blind, while the boy sings pretending to be badly injured.
This seems to work, with Ji-min taking pity on the situation in the streets.
On the yacht, the Hee-mi falls overboard while trying to smoke a cigarette, with everyone
else distracted by the music.
To her luck, a patrolling lifeguard appears, but in his attempt to rescue her, he knocks
her out and jumps into the water to get her.
As he does so, Hee-mi becomes desperate and begins to choke him, but he knocks her unconscious
and manages to save her.
He gives her mouth-to-mouth resuscitation, but the girl wakes up and bites his lip, so
the lifeguard hits her again to knock her out.
On the shore, Man-Sik greets Yeon-hee and hands her a bag full of vegetables.
The two talk about Seung-hyun's whereabouts, and Man-Sik receives a call from the police
station, where he discovers that his son was arrested for the attempted scam.
Upon arrival, Man-Sik starts fighting with Dong-choon while his son cries in despair.
At the conclusion of the bitter scene, father and son go to Yeon-hee's stall to get something
to eat, where Man-sik gets drunk easily, and are visited by Hyeong-Sik, Man-sik's younger
brother, and who turns out to be the lifesaver from before.
A family compliments the boy's appearance, who reveals that Yeon-hee is not his mother,
as the real mother abandoned them.
The situations continue unfolding, with Eok-jo losing shareholders, Kim Hwi receiving news
of new tsunami activity from Japan, and Man-Sik's friends saying that his feelings for Yeon-hee
are now more than evident.
Man-Sik's mother shows up to threaten against Yeon-hee, but as usual, the man defends her.
The three yacht boys show up to eat at Yeon-hee's stall, and after serving them, she talks to
Dong-choon, whom she forces to accompany her on her daily catch.
Man-Sik shows up before they set sail, inviting the girl to a baseball game with Seung-hyun,
to which she accepts.
A group of lifeguards listens to the game on the radio, and one of them asks Hyeong-Sik
what happened to his lip.
When they tell him that the person who did that must have been crazy, Hee-mi appears
to talk.
She tells him that he should take responsibility for the injuries he caused her, and intervenes
in his call to wait for his answer.
Late at night, she tells her friends that she will be back late, as she has an increasingly
close conversation with Hyeong-Sik.
At the game, Man-Sik gets drunk again and starts insulting the batsman, much to the
embarrassment of his son and Yeon-hee.
The police make an appearance and take him out of the stadium before descending into
further conflict.
Upon returning home, he finds his mother talking to old Eok-jo, who is actually his uncle.
After insulting him before leaving, Man-Sik kicks his dog, receiving a scolding from his
mother.
At the dock, Dong-choon accompanies Yeon-hee, who receives a note from Man-Sik.
Just then, the young men from the yacht arrive and threaten Yeon-hee and tell her that she
gave poisoned food, making one of them sick.
Dong-choon tries to defend her, but the two boys outnumber him in strength.
That's when Hyeong-Sik shows up to defend his friend, beating the boys.
In bed, Man-Sik complains of a stomachache, and while trying to get some medicine, which
he mistakes for shampoo, one of his friends tells him about the conflict at the dock.
The police show up to arrest Dong-choon and Yeon-hee, both for the fight and for selling
poisoned food.
Watching them drive off in the patrol car, Man-Sik starts foaming, and is taken to the
hospital for a stomach pump.
Because of his conflict last night, Hyeong-Sik is given the job of a coastal nursery attendant,
where he attends to a crying lost girl, who claims to know her mother's number.
The girl turns out to be Ji-min, and after contacting her mother, Kim Hwi goes to pick
her up, feeling awkward about being next to his own daughter.
Eok-jo formally asks Man-Sik to move his business, but Man-Sik reproaches him that it was his
fault that the expedition from years ago went so badly, after forcing them to set sail in
adverse conditions.
The businessman has no choice but to turn to Dong-choon to convince Man-Sik, promising
him a store if he succeeds.
Yoo-jin shows up to pick up Ji-min, scolding her for getting lost.
Kim Hwi asks her not to be so harsh on the girl, but Yoo-jin reproaches the man's absence
as a father.
Right after, Hee-mi reproaches Hyeong-Sik for not telling her about his change of position,
as she had been looking for him all day.
The two share a meal, where Hee-mi mentions studying for being an actress, giving him
an acting sample too realistic for the people around them.
Man-Sik talks to Yeon-hee, and they both mention her father's memorial, remembering the first
time they met, when Man-Sik saw Yeon-hee's father as a leader.
However, in a flashback, it is shown how Yeon-hee's father was caught in the storm due to an error
in judgment on Man-Sik's part, which causes the man to self-sabotage his intentions with
Yeon-hee.
As they continue their outing, Hee-mi tricks Hyeong-Sik into kissing him and biting his
lip again, with the girl's friends spying on her from a distance, still resentful from
the dock fight.
In the morning, Kim Hwi warns his boss about the possibility of a mega-tsunami, a wave
that could reach fifty meters at least, and even reach a hundred meters in the worst-case
scenario.
If so, they should evacuate as many people as possible in just ten minutes.
At Mr. Kang's grave, Yeon-hee confesses her feelings for Man-Sik, standing by his side,
and asks her father to make the man understand the hints she always gives him.
Man-Sik breaks down in tears, apologizing to the grave of his former friend.
He and his brother meet and talk about their women’s case, unable to give each other
good advice.
As he arranges another outing with Hee-mi, Hyeong-Sik is intercepted by the yacht boys,
who beat him up and tell him never to see Hee-mi again.
After finishing her dinner, Yeon-hee talks to Eok-jo, who is happy that his project is
on track.
Apparently, Yeon-hee is the only person Eok-jo has any regard for, perhaps out of respect
for his deceased father.
As he leaves, Man-Sik arrives, who is less than pleased with the old man’s presence.
He invites Yeon-hee to a boat, where he decorates the deck with a romantic theme, and waits
for the fireworks to propose to the girl.
Despite being amused by the idea, Yeon-hee tells a nervous Man-Sik that she will think
about it, and give him an answer early tomorrow morning.
If there is a red ribbon tied to her boat, that means she would accept the proposal.
From a distance, everyone watches the fireworks in awe, except for Hee-mi, who scolds Hyeong-Sik
for missing their date, he just turns around and tells her that they should stop seeing
each other.
Dong-choon feels pressured for not having a formal job, and in the middle of a conversation
with Yeon-hee, he learns about the marriage proposal, so he decides to reveal to her the
real cause of her father's death.
The seabed near Tsushima Island begins to crack, creating an underwater fault.
The next morning, Man-Sik is disappointed to find that not only is there no red ribbon,
but Yeon-hee's boat has sailed away, leaving him stranded.
He encounters Dong-choon, who confesses telling Yeon-hee the truth about his father.
Man-Sik lunges at the snitch, but the battle is suddenly stopped by a seagull that crashes
into Dong-choon's car.
As they watch the sky, they notice how the birds seem to fly away from the area, for
they foreshadow something bad.
Kim Hwi tries to convince his boss to evacuate the entire region before tragedy strikes,
but he says that if they do, they will be a laughing stock.
He warns Yoo-jin about the threat, but she believes it is an attempt to sabotage her
career.
At sea, Yeon-hee regrets what happened, and decides to get rid of the red ribbon.
She goes to Eok-jo and tells him that she will be leaving Haeundae next week, leaving
the old man confused and sad.
The underwater break situation becomes untenable, and a state of emergency is reported, announcing
it to the entire city.
Just as Yeon-hee and Man-Sik meet, the earthquakes begin, and all the people on the beach fall
from the tremors.
Disasters start to happen, with Dong-choon and Eok-jo crashing their cars, Yoo-jin getting
trapped in an elevator and a cargo ship being capsized at sea.
Also, Hee-mi is with her suitor on the yacht, getting caught in the middle of a massive
storm.
Kim Hwi tells his boss that they must get everyone in the highest possible spaces, and
leaves to find his wife and daughter, with the latter watching from her window as the
giant wave approaches them.
The beach gradually runs out of water, with people running for shelter and causing havoc
in the city.
Man-Sik and Yeon-Hee flee too, with the wave forming behind them, of a size that can cover
almost the entire region.
Dong-choon meets Seung-hyun and his grandmother in the middle of a bridge.
He tries to help them, but the lady goes into a catatonic state, and no matter how hard
they try to run, they cannot outrun the wave behind.
The tsunami covers the coasts, the streets and destroys the buildings, reaching the highest
floors, with no place to take refuge.
Everyone runs as fast as they can, but the end is inevitable, and in less than ten minutes,
all of Heundae is engulfed in a blanket of water, leaving only the tallest buildings
standing.
Dong-choon walks on the bridge, seeing the debris beside him and looking for Seung-hyun,
but then realizes that right next to him is the cargo ship, now hanging vertically on
the bridge, about to fall.
He manages to dodge all the cargo that is bearing down on him, but many people are not
as lucky in the city.
Man-Sik and Yeon-hee try to quickly climb a light pole before a piece of electrical
equipment falls near them.
In the distance, old Eok-jo also manages to save himself from falling into the water.
Meanwhile, Kim Hwi goes to look for Ji-min in her apartment, which is completely flooded.
He manages to catch her just before she falls into the void, being on the second to last
floor of the building.
Hyeong-Sik goes in the helicopter to rescue the distress calls on the high seas, and comes
across Hee-mi and her suitor, who makes their rescue more difficult by panicking.
Seeing that he is a burden, she decides to knock the guy out in the same way Hyeong-Sik
did when they first met.
She manages to be rescued, but Hyeong-Sik tells her that he must stay to rescue the
unconscious man.
Yoo-jin, still in the elevator, manages to communicate with Kim Hwi and her daughter
on the roof, telling them about her situation.
Yoo-jin confesses to Ji-min that the man next to her is her real father, cutting off the
call as she gets drowned down.
Father and daughter fear the worst, unaware that downstairs, the building's janitor manages
to open the elevator door, rescuing Yoo-jin in the process.
On the bridge, Dong-choon manages to save a cigarette, but after a careless attempt
to light it, he accidentally throws his lighter into a fuel leak on the ship, setting off
a chain reaction that causes everything to explode, with tons of debris falling into
the city and adding to the danger.
While being rescued, Hee-mi's suitor becomes desperate and falls back into the water, with
Hyeong-Sik coming to his rescue despite Hee-mi's warnings in the helicopter.
The situation is quite tense with Man-Sik and Yeon-Hee, as the former manages to climb
up, but falls into the water, and although his beloved holds his hand, he can't help
but slip, confessing his love as a last gesture before leaving.
Yeon-hee watches in horror as Man-Sik is swept away by the current, but just then Eok-jo
appears, grabbing Man-Sik with an injured arm to avoid his path.
He manages to rescue him, and as he gives a smile to his nephew and Yeon-hee, he is
rammed by a giant sign, carried away by the current.
During the helicopter rescue, the rope holding Hyeong-Sik and Hee-mi's suitor breaks a little
because it can't support so much weight, so Hyeong-Sik makes a strong decision.
He decides to sacrifice himself, asking his rival to give Hee-mi his watch, which she
always liked.
Despite the cries and pleas, the lifeguard ends up making the ultimate sacrifice, smiling
from the surface at his beloved, only to be swept away by a wave.
At the top of a building, Yoo-jin is reunited with Ji-min and Kim Hwi, but they see another
wave approaching in the distance, so they tell the rescue team that they are with a
little girl, so they must give priority to save her.
They manage to get a lady to hold her, but the parents can only watch their daughter
soar through the air, saying goodbye forever.
The pair share one last hug, with Kim Hwi apologizing for everything.
The rescuers go back over the buildings’ roofs, and Dong-choon along with Man-Ski's
mother, watch as Seung-hyun struggles to swim, trying to save him.
Some time later, a service is held to honor the rescuers who gave their lives for the
city, including Hyeong-Sik.
Among those present are Man-Sik, his mother and son, Yeon-Hee, Hee-mi and her friends
who were able to survive, with her keeping Hyeong-Sik’s special watch.
Murals are made to honor the fallen, including Eok-jo, Kim Hwi and Yoo-jin, and on the beach,
Ji-min and Seung-hyun talk about what happened, with her asking him if they had met before,
not remembering the scam from the beginning.
The boy tells her no and they part ways.
As they clean up, Man-Sik's friends comment on how old Eok-jo canceled his contract on
behalf of the merchants in the area, about how Dong-choon's mom perished while buying
a pair of shoes for him, and that Dong-choon received an award for saving several people
during the disaster.
Dong-choon mourns the loss of his mother holding a picture of her.
Man-Sik and his family go to his aunt's house, where his mother gives them life advice and
hugs Yeon-Hee, forgiving her for everything.
At the dock, Yeon-Hee sees the debris of her tent, and finds the red ribbon from earlier.
Man-Sik intercepts her and steals the ribbon, but it slips away and flies with the wind
to the sky.