Hee-jae watches the boat that's taking Hwi away until she can no longer see him. When she turns around, Sun-ho is there, and she asks if this is his father's doing. He says that he asked his father to bribe the examiner, but Hee-jae interrupts him with a slap, knowing that's a lie.
Sun-ho tells her to forget Hwi, but she asks if Sun-ho can do that. He says that he will, because he has to. Hee-jae says with disdain that if their positions were reversed, Hwi would do everything he could to save his friend, "Even if you'd been dragged to Hell."
Three months later.
Chief Park congratulates a colleague on his promotion to captain of the Liaodong Expeditionary Army, and he asks to be made deputy captain. Later he unpacks a set of heavy armor and touches it reverently.
We're told that the expeditionary army consists of over fifty thousand soldiers and twenty thousand horses. Lord Nam promises to make sure General Yi Seung-gye's family is safely hidden, but General Yi says that that will make General Choi Young suspicious of him. Lord Nam is more worried about General Yi's second wife, sure that General Choi will target her first.
Hee-jae has been looking for Yeon, Hwi's younger sister, but her gisaeng friend Hwa-wol says gently that Yeon is probably dead. Hee-jae is planning to leave Ihwaru gibang, and Hwa-wol asks why, when she's so close to seeing her mother again. Hee-jae says that she's tired of letting Lady Seo run her life.
Sun-ho has come to see her, dressed in his armor as he's preparing to go to war. Hee-jae advises him to be a bit cowardly in order to survive, then adds, "Although you're already cowardly enough." Ouch, but she's not wrong.
She asks if Goryeo will be overturned, and Sun-ho says that the king comes first, country second. He pours her the last drink, which is traditionally for "the one in your heart." Hee-jae understands what he's implying, but she says firmly, "My last already went to Hwi." Sun-ho says he knows, but he still wanted her to know how he feels.
General Yi's army sets out for Liaodong, and he tells Lord Nam that the king and General Choi sent advance troops secretly. He scoffs that the advance troops are not trained soldiers, and will probably die before the main troops arrive.
Hwi is one of those advance troops, and we see them on the battlefield. Hwi is injured but he manages to avoid death, though he's shocked by the horror all around him. At one point he's nearly killed by an enemy, and he's only saved at the last second by none other than Chief Park.
Chief Park tosses Hwi a bow and tells him to snap out of it, so Hwi picks up some arrows and follows him. They fight in tandem, watching each other's backs, with Hwi plucking arrows from the bodies of dead soldiers when he runs out.
Eventually the battle ends, and the captain walks the field marking down which of his soldiers are dead. One young man is badly injured, but the captain orders his man MOON-BOK (In Gyo-jin) to write him down as dead.
Despite his own injury, Hwi insists on doctoring the young man's wound. The young man pleads for help, crying that he needs to take care of his old, sick grandmother. Hwi says that he also needs to survive for his sister, so they can go home together, but the young man spits up blood and dies.
The captain sneers that Hwi looks like a dead man, too, and offers to go ahead and put him on the list. Hwi retorts, "Just wait. I will be sure to outlive you by at least one day. If you want to kill me, draw a mark for yourself as well."
Hwi walks away to be alone, his thoughts filled with memories of home. He still carries the cloth that Hee-jae used to bandage his head, and he sits for a long time just holding it and thinking of her.
Eventually, General Yi's army arrives at the base camp. While surveying the advance troops, Sun-ho thinks he sees Hwi and runs to him, but it's just another soldier who resembles Hwi.
Sun-ho reports to General Yi that the soldiers are experiencing a dysentery outbreak and many are deserting, and that the archers can't fight because their bowstrings are coming loose from melted glue. General Yi approves of his candid advice.
At the advance army camp, the captain orders Hwi to infiltrate the enemy and kill their general. Hwi argues that it's a death sentence, but he has no choice. Chief Park volunteers to go with Hwi, and the captain tells Chief Park to behead Hwi if he tries to defect.
The two head to a lookout point where Chief Park offers Hwi his horn bow, which can shoot farther than Hwi's. They identify the general's tent, and Hwi readies his bow. Chief Park advises Hwi to add five steps to his distance since the wind is blowing behind him, and Hwi freezes — it's the exact same instructions his father gave him when he was a child.
Hwi follows the advice and his arrow strikes the general's tent, drawing him out into the open. Chief Park steadies Hwi's shaking hand as he draws his second arrow, then Hwi lets it fly, and his arrow meets its mark in the general's neck. He and Chief Park run from the soldiers who try to catch them, and Chief Park continues to instruct Hwi as they enter a narrow trail purposely to slow down the enemy's horses.
When their pursuers are forced to ride in a line, Hwi starts shooting the soldiers off their horses and Chief Park closes in to finish them off. Hwi grapples with one soldier on foot, and when Chief Park sees another galloping towards Hwi, he throws himself in the path of the sword.
Hwi kills his opponent, shoots the last soldier, then turns to see Chief Park on the ground. He tears open Chief Park's sleeve to check his wound, and he's stunned to see that Chief Park has the same snake tattoo that Hwi's father, Seo Geom, wore. Hwi demands to know who Chief Park is, and Chief Park croaks, "The leader of the Black Snake Unit, which belonged to the former Northern Punitive Force. My name is Park Chi-do."
Hwi carries Chi-do (he saved Hwi's life… he's earned his name) back to camp and reports to the captain that he shot the enemy general. The captain sneers that the only witness to corroborate Hwi's claim is practically dead, and he even accuses Hwi of injuring Chi-do to hide a lie.
Moon-bok snaps at the captain to stop talking nonsense, and his buddy Jung-beom backs him up. Hwi thanks Moon-bok and Jung-beom, but they counter that they should be thanking him. They carry Chi-do to his tent, where Hwi watches over him.
When he wakes, Chi-do points out the set of armor he brought and says it belonged to Hwi's father, and that Seo Geom asked him to give it to Hwi when he was old enough. He tells Hwi, "He was always so proud of you, and he always missed Yeon."
Hwi's breath hitches, then he applies himself to repairing the armor, which is engraved with his and Yeon's name, just like his bow. Tucked into a small tear in the armor, Hwi finds a piece of paper that's been stamped, but nothing is written on it so Hwi puts it back where he found it.
The next time the gisaengs gather to pass information to Lady Seo, Hee-jae instead tells Lady Seo that she will no longer be used after Lady Seo used information she brought to kill her friend. She vows to become the one who receives information, not someone who collects it, and that she'll use that information to punish those who do wrong to her and others.
She says she'll leave now, and rises her her feet. She tells Lady Seo, "I will die outside these premises, so I hope you live a long, healthy life here at Ihwaru." Lady Seo suddenly suffers a coughing fit, and she gasps to Hee-jae that everything happened because she wanted it, so she can't blame anyone or regret anything. Hee-jae whispers that she'll carry no regrets or blame, then she leaves.
Outside, Hee-jae asks Gyeol, Lady Seo's bodyguard, how long she's had that cough. He says it's been ten years, and that Lady Seo always stifled her cough in front of Hee-jae. He tells Hee-jae that he killed the man who ate her friend's sister's liver (supposed to cure leprosy), and that Hwa-wol's stepfather, who sold her to the gibang, died of lung disease. As for those who killed Hee-jae's mother, Gyeol promises Hee-jae that he'll find them no matter what.
Hwa-wol catches up to Hee-jae and gives her some food, then cries that Hee-jae is mean and heartless (for leaving). Hee-jae asks her to tell Hwi where to find her if he ever comes by, then she leaves for good.
After being at the front line for a month, Lord Nam and General Yi realize that illness and deserters are getting worse. General Yi hopes that the advance army will have a competent leader, but Lord Nam says that their captain is the most incompetent leader they have. General Yi growls that it doesn't have to be him, and Sun-ho looks at him thoughtfully.
The advance army's camp is ambushed, and for the first time, Hwi dons his father's armor. He slices through the enemy army like a deadly whirlwind, screaming orders to his fellow soldiers as he goes. The enemy have the advantage with their horses, so Hwi calls for Moon-bok and Jung-beom to cover him as he targets the mounted soldiers.
At one point during the battles, Hwi looks up to see an enemy archer aiming right at him. He readies an arrow, but nearby, a soldier knocks Moon-bok down and raises his sword to kill him. With only an instant to choose, Hwi swivels and kills Moon-bok's attacker, then is shot in the shoulder by the archer.
Unable to handle his bow, Hwi grabs a sword and charges at the archer, leaping into the air and slashing his throat. Moon-bok starts screaming joyously — that was the enemy's new general, and the Ming army turns and flees.
Hwi is surrounded by his fellow soldiers, the arrow still sticking out of his shoulder. Their captain orders them to charge, but the soldiers wait for an order from Hwi. He breaks off the arrow in his shoulder, then bellows, "Soldiers… CHARGE!"
After the battle, Moon-bok and Jung-beom find Hwi digging a grave for their dead, and they tease him for acting like a "fake lieutenant." Hwi says he's just doing what he can to stay alive and earn his way out of the army so that he can go home to his sister honorably.
Jung-beom takes over digging so that Moon-bok (who used to be a mortician) can look at Hwi's injury. He stitches up the arrow wound, and Jung-beom brings Hwi some "medicinal" wine to pour on the area. Moon-bok swipes it and takes a slug, then dares Jung-beom to drink, so he does… and falls over, hee.
That evening, Hwi tells Chi-do that they only have seventy-five able fighters left, and the main army is still stuck across the river. Chi-do says that this is the purpose of an advance army — to fight and die first.
Meanwhile, Hee-jae makes her way to the home of Lady Kang, General Yi's wife in Seoul, who is considered as wise and honorable as any general. Oddly, the gates are open and the home seems deserted. Hee-jae lets herself in to look around, and she's grabbed from behind and a knife held to her throat.
A female voice asks who she is, and Hee-jae says, "You should light the furnace. Unless there's smoke, people will think the house is vacant. Keep the gates open, too — if closed they'll jump the wall." She offers to sere Lady Kang until the conquest is over, and to protect her life with her own.
LADY KANG (Park Ye-jin) shows her face and asks Hee-jae why. Hee-jae says that she believes Lady Kang can get her to a position that's too good to be true — beside the queen. Lady Kang warns that protecting her will put Hee-jae in danger, but Hee-jae says that she trusts Bang-won to reach Lady Kang before General Choi's assassins.
Lady Kang asks why General Yi would send Bang-won out of all six of his sons, and Hee-jae says that Bang-won is the only one who can fight off assassins… and that General Yi has eight sons. The two youngest are hiding behind the screen, and when they come out, Hee-jae introduces herself.
Hwi and Jung-beom sit on an outcropping, looking across the river at General Yi's camp. Hwi says that they'll retreat if the king dies, if there's an assassination attempt, or if someone tries to take the throne.
Hwi writes a note that only seventy-five of the five hundred advance soldiers are still able to fight, then sends it over the river tied to an arrow. The arrow buries itself into a post only inches from Sun-ho's head, and a short while later, an arrow flies the other way with a note asking how long they can hold out.
Hwi replies that they can only hold out until they're dead, and Sun-ho answers that he'll relay the message. His note asks the sender's name, but Hwi's response arrives after the officers are summoned to General Yi's tent for orders.
The officers discuss the fact that Goryeo has become a country of corruption and their plans for rebellion. General Yi warns against assassinating the king, because they need to paint him as a coward in order to turn the people against him. He formally declares his intent to disobey the king's orders to fight this war, and to retreat.
Hwi and Jung-beom wait in the rain for a response from the main camp. Unfortunately, it's not Sun-ho who receives his message with his name on it — it's Lord Nam. When Sun-ho asks who was sending the messages, his father lies that the rain washed away the ink.
Sun-ho reports to General Yi about the advance army's dire situation. Lord Nam argues that the remaining seventy-five men are lowlifes, and even Sun-ho agrees that sacrifices must be made in a revolution. General Yi argues that they are also citizens of Goryeo, but Sun-ho accuses him of only trying to appear compassionate.
General Yi makes his decision, and tells his lieutenant, Sung-rok, to form a death squad to cross the river and make sure there are no survivors. He orders Sun-ho to go along, saying that if he accomplishes this, he'll keep Sun-ho at his side. He offers Sun-ho his sword, and this time when Sun-ho appropriately kneels to accept, General Yi tells him to stand.
Concerned that General Choi will go after his family, General Yi entrusts Lord Nam with a note instructing Bang-won to escort his mothers to a safe area. Lord Nam asks why he's not sending his eldest, Bang-woo, and General Yi says that, regardless of the order of their birth, he considers Bang-won his "first" child.
Bang-won plays drinking games with his men at Ihwaru gibang. Hwa-wol complains to Gyeol that Bang-won is acting immature while his father is at war, but Gyeol notes that Bang-won and his party aren't actually drunk — their weapons are within reach and they're spread out to keep an eye on all parts of the property.
The message from General Yi arrives, and sure enough, Bang-won and his men are suddenly quite sober. Bang-won orders Cheonga to escort his mother, while he and Tae-ryong will travel to Pocheon for "the bitch" (Lady Kang) and will meet up with them in Hamhung. He warns CG that General Choi will be after him, and that if his family dies, his father's revolution will fail.
When Bang-won arrives at Pocheon, Hee-jae knows who his is by his signature red arrows and his "eyes of a dragon." Bang-won introduces himself in banmal to Lady Kang, who isn't pleased that it took him this long after news of the rebellion to arrive. She insists he call her "Mother," refusing to move unless he shows her some respect.
He does, though with obvious disdain. Bang-seok, the youngest of Lady Kang's sons, says hello to his hyung-nim, but Bang-won smirks, "Who says I'm your hyung?" Lady Kang says that she knows why General Yi sent Bang-won — as an example of how not to raise her sons.
The advance army realize that there's trouble when they notice General Yi's army preparing to retreat. The captain dismisses Hwi's warning, sneering that he's only a lieutenant because there's nobody else left. Hwi yells that the captain sees them as dispensable, so the caption grabs a piece of firewood and begins beating Hwi for insubordination.
Hee-jae's cloth falls from Hwi's clothing and the captain picks it up, assuming Hwi stole it. He tosses it into the fire, and Hwi immerses his entire arm into the fire to get it back. Furious, he grabs a sword and advances on the captain, who starts stammering promises to recommend Hwi for a real promotion.
He claims that he's taken an interest in Hwi, giving him credit for their survival. Hwi growls, "Then what's my name? Do you even know any of our names?" Of course the captain doesn't, so Hwi raises his sword… but Chi-do stops him.
Back in his tent, Hwi cries as he holds his salvaged cloth and thinks of Hee-jae. He hears her voice telling him, "Don't let anyone oppress you. Only then will you not collapse. Don't let anyone intimidate you, even if they're stronger than you. Only then can you hold out."
Lord Nam gathers a party and orders them to kill every surviving member of the advance army, and to burn their boat and die honorably if anything goes wrong. He watches his son march away, unaware that he may be about to face Hwi for the first time since betraying him.
Meanwhile, Moon-bok asks Hwi what he plans to do about General Yi's retreat. Hwi says it's not like they can kill the captain and flee, but Jung-beom doesn't see why not, since dying is their only other option.
Chi-do overhears their conversation and decides to take matters into his own hands. He slips into the captain's tent and stabs the sleeping form on the dais… but the captain has already deserted and is making his way towards the river, having been informed of a small messenger boat.
Unfortunately for him, the captain encounters Sung-rok and his party on the way. He's relieved to see Sung-rok for about three seconds, until Sung-rok skewers him and his accomplice then continues on to the camp.
The party takes out the advance army's sentries, then split up to dispatch the sleeping soldiers. They manage to kill a few before they run into Chi-do, and Sung-rok says he's come to deliver a message. Chi-do asks for the watchword, and Sung-rok snarls, "Slaughter," as his men attack.
Chi-do fights them off while yelling that they're under attack. The advance army is only stunned for a moment before they begin fighting in earnest, but Sung-rok and Sun-ho fight heartlessly, taking down many of their own countrymen without hesitation.
Hwi is on the other side of the battle, bravely facing the men who came to kill him and his fellow soldiers. At one point, Hwi watches as Moon-bok is injured, so he rushes over to fight off Moon-bok's attacker.
Their swords clash… and Hwi and Sun-ho both freeze in horror as they see each other for the first time in months.