King overpowers and single-handedly defeats Guila using his Sacred Treasure, the Spirit Spear Chastiefol. As Meliodas, Elizabeth, Hawk, Diane, Ban and King return to the village, King tells the others that the Sacred Treasures of the Seven Deadly Sins unlocks each of their full potential in combat. However, Meliodas sold his, Diane lost hers and Ban got his stolen. Meliodas, Ban and King head to the Merchant Town Vaizel during the annual fighting festival, in which the grand prize happens to be Diane's Sacred Treasure, the War Hammer Gideon. Meanwhile, Great Holy Knight Hendrickson summons Jericho and Twigo underground, offering them blood from the corpse of a red demon as a means of enhancing their strength. Twigo explodes after drinking the blood, but Jericho manages to survive the excruciating experience.

Gowther is welcomed by the others into their group, but he soon finds out the true secrets behind them by delving deep into their memories and emotions. Meanwhile, Hendrickson and Helbram have the hilt of Meliodas's sword in possession, in which they plan to use it as a fragment of a ritual relic, known as the Coffin of Eternal Darkness, to resurrect the red demon race as a means to start a holy war. At the Boar Hat, Holy Knight Vivian suddenly appears and kidnaps Elizabeth and Hawk. Diane throws Meliodas, Ban and Gowther toward the Kingdom of Liones, where the three are bombarded by an army of Holy Knights on the north side of the castle. However, Arthur Pendragon, the young king of Camelot, has approached the south side of the castle with his own army.

Hendrickson tries to convince Arthur to leave the castle, but to no avail. Instead, Hendrickson escorts Arthur inside the castle and suddenly engages him in battle. Meanwhile, Elizabeth and Hawk are teleported inside the dungeon of the castle, and they try to find a way out. Meliodas, Ban and Gowther manage to defeat the army and sneak inside a town of the kingdom, while King summons his black hound Oslow to use its mouth to teleport Diane inside the castle. However, Diane is attacked by Guila, Jericho, Gilthunder, Howzer, Helbram and Great Holy Knight Dreyfus. Diane tries to defend herself, but Dreyfus overpowers her with an attack that sends her crashing onto the town streets. After Diane wander the streets and protects Zeal from being crushed by a falling building, both Howzer and Guila switch sides to defend Diane.

The combined powers of Howzer and Guila have little to no effect. When Dreyfus attacks Guila, Gowther saves Guila in the nick of time and faces Dreyfus alone. Meanwhile, Elizabeth and Hawk encounter Margaret Liones, Elizabeth's eldest sister, in a cell. Vivian appears, teleporting Hawk elsewhere, knocking Elizabeth unconscious and releasing Margaret from her cell. Gowther traps Dreyfus in a nightmare, but Dreyfus somehow snaps out of it and pierces Gowther in the chest. Once a heavily injured Dreyfus leaves with Gilthunder, Helbram attempts to finish Diane off, but King appears and stops Helbram, who reveals himself as a fairy and King's former best friend. Helbram uses his magical tree roots to restrain King and inflict brutal lashes on Diane. However, King uses Chastifol to shield Diane from getting hurt. King says that he is fulfilling a promise that he made seven hundred years ago.

Gilthunder leaves Dreyfus to fight Meliodas alone, while Hendrickson deals with Arthur and ultimately defeats him. Meanwhile, Elizabeth wakes up in a chamber and finds her father, King Bartra Liones. Meliodas then finds himself outmatched against Gilthunder, Hendrickson and Vivian. At the same time, Margaret decides to take her own life by jumping off a castle tower. Margaret and Gilthunder are both released from their curse in the form of monsters, thanks to Meliodas. While Margaret is thus saved from falling, Hendrickson tries to finish Meliodas off, but Gilthunder stands in the way and knocks down Hendrickson at full force. Vivian tries to trap Meliodas, Gilthunder, Margaret and Arthur in illusionary places, but Merlin, the Boar's Sin of Gluttony, makes her first appearance and breaks the spell.

Ban explores the catacombs under the city. Merlin and the other sins go to the chamber where the king Baltra and Elizabeth are being held captive. Dreyfus has a confession.

Ban attempts to kill Meliodas, but is stopped by Hawk. Meliodas and the sins corner Hendriksen and prepare to take him down.

With the capital retaken and the Liones Kingdom slowly getting back on its feet, Meliodas, Elizabeth and Hawk turn their attention to the Boar Hat.

King is overjoyed to spend the day of the festival with Diane, but he's struggling to figure out how to take the next step.

As the kingdom begins to rebuild after the coup attempt, the king honors the Seven Deadly Sins for their bravery with a medal ceremony.