The third princess of the Kingdom of Liones, Elizabeth, finds Meliodas, who is the owner of the Boar Hat bar and is also one of the Seven Deadly Sins. With her identity revealed, she is pursued by Twigo whom Meliodas easily defeats. The princess joins him on his journey to find the other Deadly Sins in order to defeat the Holy Knights, who have orchestrated a coup d'état and have overthrown the king.

Meliodas agrees to help Elizabeth, revealing how his business has been travelling from place to place to acquire information about the rest of the Seven Deadly Sins as well and letting her join him. The two, along with Hawk, soon stop over at the Bernia Village, a village famed for their delicious Bernia ale and its primary source of income. However, a Holy Knight Gilthunder has planted his sword in the center of the town, stopping all water sources. Despite the villagers' futile efforts, Meliodas easily removes the object and is hailed as a saviour of the Bernia Village. Gilthunder, wanting to confirm whether the removal of his sword was an accident or not, throws a spear imbued with his power towards the town, which is reflected back in the same direction by Meliodas, destroying Fort Solgales, Gilthunder's current location, and missing his head by centimetres.

Meliodas, Elizabeth and Hawk travel to the Forest of White Dreams, a foggy, dense forest where even the Holy Knights avoid. Inhabiting the forest are Prankster Imps, which harbour shapeshifting abilities that confuse travellers by impersonating their companions. After defeating the Prankster Imps, they find a Giant girl asleep in the forest, who introduces herself as Diane, a member of the Seven Deadly Sins who possesses the Serpent's Sin of Envy, declaring her crush on Meliodas. This surprise reunion is soon interrupted when Gilthunder arrives, binding all of them with his lightning magic and facing Meliodas in a one-on-one fight, where the latter is dealt a severe injury. Under the pretense of dying, he acquires information about the whereabouts of two members of the Seven Deadly Sins, Ban and King, as his apparent last wish, tracing their locations to the Baste Dungeon and the Capital of the Dead respectively.

Diane throws Gilthunder out of the forest and decides to accompany Meliodas, Elizabeth and Hawk on their travels. Their next stop is Baste Dungeon, where Ban, the bearer of the Fox's Sin of Greed, has been imprisoned for five years. However, Meliodas collapses suddenly from his injury and they decide to stop at Dalmary Town, letting a doctor named Dana treat him with medicine. There, Diane and Elizabeth both show care for Meliodas, but display envy towards each other due to their opposites in strength and size, with Diane ultimately deciding to leave to find Ban herself. Unbeknownst to them, Dalmary Town is currently under the rule of the Weird Fangs, a unit in the Holy Knights, who are determined to kill Meliodas and Diane, and capture Elizabeth. Dana also unexpectedly reveals to a shocked Elizabeth that the supposed medicine he administered is a deadly poison, while Golgius, a member of Weird Fangs, appears out of the blue to escort her back to the Kingdom of Liones.

As Meliodas and Diane continue to fight each other under hypnosis, the fourth and final member of Weird Fangs, Friesia, attacks the disguised Ruin with her insects, prompting Elizabeth to risk her life to protect him. However, as Ruin reveals his true identity, he realises that Elizabeth was going for the bell on his staff the whole time, successfully freeing Meliodas and Diane from the spell to defeat Ruin and Friesia respectively. Meliodas, Hawk, Diane and Elizabeth, who is being carried in Diane's bag, infiltrate Baste Dungeon to rescue Sennett, and find Ban wandering around the prison as well with no sign of having been injured, causing the dungeon's collapse during their happy reunion and breaking a secret barrier that Golgius set up in the process. The six of them regroup back at Dalmary Town, where Dana, who survived the attack, treats them to a meal as courtesy. Meanwhile, King, the bearer of the Grizzly's Sin of Sloth, is shown to be allied with Gilthunder and the rest of the Holy Knights.

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.

With his true power finally shown, Meliodas clashes with Helbram, who takes note on how Meliodas hones his dark abilities. After managing to defeat Meliodas, Helbram steals Meliodas's sword. Ban takes Elizabeth, Hawk and King to safety, while Diane returns to her normal size and wields Gideon with attacks that crumble the earth, forcing Helbram to retreat with Guila and Jericho in tow. Elizabeth embraces Meliodas after he is rescued by Diane, later lamenting the death of Veronica. Ban and King express their motives behind taking back the kingdom. With his sword now stolen, Meliodas vows to end the ongoing war once and for all.

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.

Hendrickson unveils the source of his power, the corpse of a red demon, which is the same one that Ban slayed in the Fairy King's Forest long ago. After Ban pummels Hendrickson through the ground, Meliodas, Ban, King and Gowther jump down the hole to a cave, where Hendrickson injects himself with the blood from the corpse of a gray demon to acquire even more power. A sudden burst of energy from Hendrickson sends the four of them back above ground, where Hendrickson easily overpowers all of his opponents despite all of their efforts. With Meliodas left standing and protecting Elizabeth, Hendrickson casts a large dark blast, but Hawk sacrifices himself in order to save the two of them. Shocked of losing her dear friend, Elizabeth awakens her dormant powers that repels Hendrickson and heals everyone else. However, Hendrickson survives and still has strength left in him to fight.

The Seven Deadly Sins and the Holy Knights all combine forces in an attempt to defeat Hendrickson. Meliodas, given support from his friends and allies, uses his ultimate technique to finish Hendrickson off. When Bartra appears with Merlin, he commands the Holy Knights to restore the kingdom and preserve its people as their "punishment" for starting a holy war. Bartra then thanks the Seven Deadly Sins for saving the kingdom and protecting Elizabeth. Hawk is revived as a piglet, much to a surprise. Things return to normal inside the kingdom, and a festival is held at night. The next day, Elizabeth joins Meliodas, Hawk, Diane, Ban, King, Gowther and Merlin in finding the last member of the Seven Deadly Sins, Escanor, the Lion's Sin of Pride.

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.

Ban and Meliodas meet to continue the duel they left unfinished before, only to find that Hawk has told everyone about their solemn battle.

Business at the Boar Hat is dropping, so Meliodas asks Merlin to join the staff as a waitress alongside Elizabeth and Diane to attract customers.

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

With Fraudrin's manipulation of Hendrickson, the Ten Commandments return to the physical realm. King follows Ban to the Fairy King's Forest.

Diane confronts Gowther after he manipulates Guila and Zeal's memories. With the return of the Demon Clan, new threats descend upon allied clans.

The fairies reconcile their differences with King as Ban leaves the forest. Meanwhile, Meliodas and gang are overwhelmed by the sheer power of Galand.

Hendrickson, thought to have been defeated against Meliodas, aids Gilthunder and the Holy Knights against a powerful Gray Demon.