In 1388, the first king of the Joseon dynasty turned his army around at the right moment
and defeated the last pillar of the Goryeo dynasty. Goryeo generals who felt the threat
stole the kingdom's treasures and fled far out to the sea, never to be seen again. Four years later,
a group of thieves led by Moo-Chi are drifting at sea on top of a piece of wood after escaping
from a bunch of soldiers that wanted to capture them for stealing from the palace.
Fortunately, they're found by Captain Hae-Rang and her pirate ship, who rescue them and take them in.
When he first sees her, Moo-Chi thinks Hae-Rang is a beautiful angel. However, four months later,
he's learned how strict she is. Things are tense between both groups: the pirates think the thieves
are lazy and gross, while the thieves think these aren't real pirates because they don't target
merchant chips, only Japanese pirates. There's also the fact that the thieves don't know if
listening to Moo-Chi because he's their boss or to Hae-Rang, because they're on her ship. One
afternoon, they find another Japanese pirate ship and get ready to attack. Eager to show he's useful
and talented, Moo-Chi jumps ahead first, easily defeating their opponents with his advanced sword
skills. Hae-Rang's crew takes over the Japanese ship and while the enemy leader refuses to talk,
one of their kids is so scared that he confesses they were looking for a big treasure. Luckily,
the map has already been found by one of Hae-Rang's men, and they discover this
treasure is supposed to be the one Goryeo generals stole years ago. All the men want to go after it,
and after some hesitation, Hae-Rang accepts. Eventually, the group makes it to an island,
where Moo-Chi takes over guidance because Hae-Rang is having trouble reading the map.
When they suddenly see a cow, Moo-Chi sees it as a welcome sign and goes after it with his bandits,
but this turns out to be just the first cow in front of a herd and the guys are run over.
Moo-Chi is pushed off the cliff, and while the group thinks he's dead, he's actually fine and
hanging on a branch, where he finds an old tusk. When he climbs back up, Hae-Rang immediately grabs
the tusk because she remembers one drawn on the map, and finds the real map carved on the bone.
Before going after it, though, they have to take care of the cow-inflicted wounds. Hae-Rang is
tired of dealing with the thieves' bad decisions and explains she only took them in out of pity,
but now they're back on land, so if they want to keep traveling with them,
they must become pirates under her command. Moo-Chi refuses, thinking his men will back him
up, but they all join Hae-Rang and Moo-Chi is left on the island. Meanwhile, the remaining leader of
the Goryeo dynasty is trying to get back to power and hires the legendary General Heung-Su for help.
Heung-Su explains that before soldiers he'll need riches, so their best bet is to find the mythical
treasure. Back on the ship, the crew is having a banquet to celebrate their success, only to find
out that the tusk has been stolen while they were distracted. A note left behind indicates Moo-Chi
is the culprit, so Hae-Rang takes a few men with her back to the island to recover the tusk. After
a dangerous encounter with a tiger, Hae-Rang finds Moo-Chi in an abandoned shack and fights him until
he confesses that actually, it was thief Mak-Yi that took it. It turns out Moo-Chi did go back
to the ship in the middle of the night to steal the tusk and Mak-Yi helped him, pretending he
was still loyal to his boss. But as soon as they made it to the shore and Moo-Chi turned around,
Mak-Yi stole the tusk again and took it with him. To make matters worse, Mak-Yi escapes the ship and
goes to the mainland to try to sell the tusk to a rich merchant while pretending to be Moo-Chi.
Fortunately, the crew shows up just in time to stop the sale and take the tusk back,
they also kidnap the merchant's daughter because she had been helping Mak-Yi. Once they return
to the ship, Hae-Rang decides Moo-Chi, Mak-Yi, and the girl shall be punished with death. But
when Moo-Chi is about to be executed, he reveals he's been hiding a knife all along and manages
to escape. He gets inside Hae-Rang's office and steals the tusk to then hold it above the water,
threatening to drop it if they try to hurt him. Hae-Rang puts her sword down and accepts not to
kill anyone if she's given the tusk back. Moo-Chi does give it to her, only to be pushed into
the water after Hae-Rang reveals she's always known about his dagger and she only wanted to
re-establish her leadership by reminding them she could kill them if she wanted. Moo-Chi and Mak-Yi
are sent to do manual labor while Hae-Rang and her men take off the piece of cloth covering the tusk,
but the message on it is encoded and they don't know how to read it. Meanwhile, General Heung-Su
tortures a priest into revealing the location of the treasure and asks the dynasty leader to
be named the next king if manages to find it, but his request isn't well received. Back on the ship,
Hae-Rang allows Moo-chi to look at the cloth and he manages to read the message, which says their
next destination is the island of Haegildo. This is a very dangerous place nobody has come back
from and Moo-Chi doesn't want to go, but Hae-Rang thinks it's worth the risk. She takes a few men
with her in a boat, each of them carrying a pig bladder filled with air before jumping into the
whirlpool that takes them to the cave mentioned by the tusk. Moo-Chi doesn't know how to use his
bladder and almost drowns, so Hae-Rang has to drag him out of the water and give him mouth-to-mouth
to help him survive. The cave seems to be empty, but while everyone is ready to give up,
Moo-Chi notices something and is rude to Hae-Rang just to provoke her right-hand man into a fight.
By throwing the guy against a cave wall he makes it break, revealing a hidden path. The group
follows this path and is happy to find a bunch of chests, only to get disappointed again when inside
they only find some old bottles. There's also a strange flag with a monster head painted on it,
but most interestingly, there's some code inside its mouth. Before they can decode it, though,
something explodes and makes the cave shake. It's General Heung-Su and his men, who have arrived at
the island and are entering the cave from above instead of having to struggle with the whirlpool.
A fight starts between both groups and Mak-Yi takes the chance to look at the flag in secret
before running away, but Hae-Rang is knocked out by the falling debris from the cave ceiling.
Moo-Chi makes the men take her away while he stays back to fight. General Heung-Su gets more
aggressive when he recognizes Moo-Chi as the former soldier that stopped him from becoming
king last time. During the war, Heung-Su had been promised kingship if he brought the enemy's head,
and to achieve that victory, he killed his own wounded soldiers. When Moo-Chi learned about this,
he snitched on him and declared him a traitor. The battle is fierce and pretty equal, so Moo-Chi
distracts Heung-Su by throwing his sword at him before jumping back into the whirlpool with all
the chests. Heung-Su tries to go after him, but without a pig bladder, he doesn't have extra air
to stay this long underwater and must go back to his men. Then, Hae-Rang shows up to help Moo-Chi,
but this time it's her who passes out because of lack of air. Moo-Chi takes some air from the
bladder and passes it to Hae-Rang mouth-to-mouth, getting to keep her alive. Before they can swim
up, however, a whale shows up and swallows them both. The crew thinks they've lost their bosses,
but soon the whale is expelling them through its blowhole and both of them safely land on the ship.
In the meantime, Heung-Su finds the strange flag and quickly understands the code, thus he
gets the dynasty leader to lend him a ship with powerful cannons to sail to the next location,
although he still needs to solve the riddle on the corner of the flag. A few hours later,
Hae-Rang has a nightmare about fire dragons and finally realizes that the code she had seen on
the flag had been a sea chart. She leaves her room and announces that they must go back to
get the flag because it has the map to the next location. However, the girl quickly cuts in and
lets everyone know Mak-Yi had seen and understood the code. The crew jumps on Mak-Yi and ties him
up to make him confess what the code said, which turns out to be Inazuma Island, a place surrounded
by lightning. Mak-Yi thinks is too dangerous to go, yet he's the only one that knows the way,
so if the crew wants him to guide them, then he demands to be captain until they find the
treasure. Hae-Rang isn't amused but she allows the crew to vote, and when she closes her eyes,
everyone votes in favor of Mak-Yi temporarily becoming captain because they want to find the
treasure. Mak-Yi becomes captain and Moo-Chi and Hae-Rang are put on kitchen duty. Hae-Rang
is an awful cook, but nobody dares to tell her her food tastes horrible because they're scared
of her. Moo-Chi tries to tease Hae-Rang about the situation, and she snaps at him, explaining this
isn't about power. She wouldn't have minded giving someone else her position if that person actually
deserved it. She is right to think Mak-Yi is an awful captain: he bullies and insults
the whole crew, hands punishments over nitpicky details, and his orders barely make any sense.
Later in the evening, Moo-Chi invites Hae-Rang to watch the stars with him in the crow's nest
and the two of them have a lovely bonding moment. The next day, the ship makes it to an area known
as the Sea of Fire, which Hae-Rang survived as a kid and is what gives her those nightmares. The
legend says fire dragons come out from among the waves when in reality, there are small underwater
volcanoes. Hae-Rang wants to redirect the ship, but Mak-Yi refuses, claiming to know the route
better. This causes them to get closer to Inazuma Island and soon the lightning is hitting the ship,
starting a fire. Heung-Su's ship is arriving as well, and they've put up kites to redirect the
lightning and avoid getting hit. Back to the pirates, Mak-Yi is too scared and confused to
do anything, so Hae-Rang begins shouting orders again as she takes over the helm.
Mak-Yi slips off the deck and almost falls into the water but Moo-Chi saves him just
in time before Hae-Rang guides the ship out of the storm thanks to her quick thinking. Moments later,
the crew takes two boats to the island, but Mak-Yi doesn't know where to go next because he only
got to read the name of the location yet not the other details. The crew begins digging in random
spots while Heung-Su and his men also arrive at the island, and thanks to having the riddle,
they quickly guess they must climb the island's mountain, which is constantly under lightning.
Moo-Chi also notices this lightning, which always falls on the same spot, so he decides
to go investigate alone after telling Hae-Rang he's doing it for her. A few moments later,
Moo-Chi makes it to the top of the mountain, finding Heung-Su and his men already there. There
are abandoned houses everywhere and the skulls of the founders of the Joseon dynasty on spears,
but when Heung-Su's men try to remove them in search of the treasure, they're all stabbed
because it's an apparatus trap. There's only one spear left that Heung-Su takes himself and he
doesn't get hurt because that spear represents the last standing general. Meanwhile, Mak-Yi runs away
from the crew to avoid their anger and bumps into a penguin with a gold bar in its beak. He calls
the crew over and together they try to communicate with the penguin, to no avail. Suddenly, the
sound of shooting cannons distracts everyone: it's Heung-Su's ship attacking the pirate ship. Moo-Chi
also gets distracted by this and accidentally reveals himself, causing Heung-Su to send his men
after him while he opens the chest he found under the spear. Unfortunately, instead of treasure,
he only finds an old mask that matches the face on the flag. Hae-Rang is worried about Moo-Chi,
but she can't let the enemy get away with destroying their ship. With a heartfelt speech,
she gets the crew to follow her leadership again and they divide the group in two: a few of them go
up the mountain to help Moo-Chi, while the rest goes back to the ship with Hae-Rang. However,
Mak-Yi is offended that the captainship was taken away from him and he leaves with the penguin to
find the gold, putting a rope around the poor bird to follow it underwater. On top of the mountain,
the thieves arrive as backup, giving Moo-Chi the chance to steal the mask from Heung-Su
and ask him for a final duel. The fight is fierce and in the struggle, they knock the mask off,
making it fall on top of Mak-Yi's head, who immediately grabs it and discovers the last
piece of the puzzle. The mask says "enter" and it matches the shape of a cave under the island,
so obviously he must go in that direction. Inside the cave, he finds a bunch of penguins standing on
frozen land and, most importantly, the legendary ship with the treasure. Mak-Yi starts to celebrate
only to be attacked by the penguins. Hae-Rang and the rest of the crew manage to get on the boats,
but by the time they get back, their ship is already destroyed. Their archer doesn't give up,
though, and he begins attacking Heung-Su's crew with his arrows, inspiring the other pirates
to launch an attack as well to take Heung-Su's ship as theirs. It's not an easy fight because
the underwater volcanoes keep erupting around them, starting a fire on the ship,
and the enemy captain won't listen to Hae-Rang when she asks him to work together to survive.
When Hae-Rang is starting to think they have no hope left, Mak-Yi shows up in the legendary ship
together with the penguins to save them all. The crew jumps over before anyone could get killed,
but at that moment, a new whirlpool appears on the water and gets more volcanoes to erupt,
destroying the enemy ship. Fortunately, the pirates manage to get their new ship away
thanks to Hae-Rang's good use of the helm and thoughtful orders on how to handle the sails.
On top of the mountain, the storm gets worse and Moo-Chi and Heung-Su have to drop their swords
to avoid being hit by lightning. After watching their ships go down, though, their fury returns
and the battle starts once again regardless of the lightning situation. Heung-Su manages to stab
Moo-Chi, but it's not in a vital spot, meaning Moo-Chi still has a chance. One of the thieves
throws a sword at his boss and he uses it to push Heung-Su into the spot the lightning always comes
back to, instantly killing him when it hits. Hours later, everyone is back on the new ship
and their wounds are taken care of. Hae-Rang admits she may accept Moo-Chi as co-captain if
he behaves, and when Moo-Chi admits he'd follow her into the afterlife, Hae-Rang kisses him.