Before the battle, Osman raids the Byzantines and seizes ammunition, before going to battle with the support of Turkmen and Seljuk forces. During the battle, Dukas and local Tekfurs are killed by Osman's forces, with Nikola and Helen escaping alive, and Turhan Alp being martyred. Meanwhile, Zoe tries to poison the pregnant Malhun Hatun but is caught and arrested. After the battle, Osman's son Orhan is born, whilst Bala reveals to Osman that she is pregnant and Osman decides to establish a state after visiting the Aksakals.

The tensions escalate further upon the death of Argun, who was killed by Geyhatu, and Geyhatu's visit to Tabriz in order to become the Han of the İlhanlı (transl. Ilkhanate). Nikola vows to ally with the powerful Geyhatu in order to destroy the Turks. Ertuğrul also recovers and stops Savcı from becoming the Bey (which is a part of Dündar's plans) while Yavlak allies with Osman to help him against Geyhatu.

The tribe elections are held to decide the new Bey. Dündar comes face-to-face with Osman however, Osman is elected as the new Bey much to Dündar's despair and anger. Meanwhile, a new threat against the Kayı tribe emerges after Petrus, sent by the Pope, arrives to help Nikola kill Osman but also has a secret plan which he doesn't tell Nikola about. Bayhoca, Savcı's son, also returns.

A wedding ceremony is set up in Kayı Tribe for the marriage of Osman Bey and Malhun Hatun. While the wedding is being held, Bala Hatun grieves despite her consent to this marriage. With the arrival of the winter season, after the wedding ceremony, it is decided that Kayı tribe will migrate to Domaniç Plateau. While preparations continue in the tribe, Togay breaks the agreement and decides to attack Osman Bey, despite the warnings of the Mongol governor Yargucu. In the ensuing battle, Togay kills Bamsı Beyrek after a fight.

Tekfur Alexis of İnegöl seeks revenge on the Kayı tribe for conquering Kulucahisar. He invades a caravan of the Kayı tribe, Osman, takes his revenge by defeating him in a battle. After the battle, the Emperor, concerned over the Turk threat on his empire, sends Aya Nikola to İnegöl Castle. Nikola kills Alexis for his failure and snatches the castle from him. Nikola also frees an old friend from prison, Flatyos. Ertuğrul also later returns towards the end after a year in Konya.

After Nikola is stabbed by Osman, Flatyos attempts to take revenge on Osman with a gunpowder plot on Söğüt. Osman however, is aware of the attack and Flatyos' plans backfire. Flatyos is captured and is taken to Kulucahisar where the "incompetent" Dündar and Savcı are saved by Osman who were about to be beheaded by Nikola.

Targun goes to meet her father at Kulucahisar but is spotted, when she returns, Osman captures her and she is forced to tell the truth. Osman vows to help her save her father and also decides to marry her after Bala says that he needs an heir to become the Bey. He also attacks Kulucahisar while Nikola goes to meet Arslan at the Çobanoğlu tribe.

Targun and Osman make a plan to kill Nikola and rescue İnal Bey in which they succeed in rescuing İnal but fail to kill Nikola and only injure him. Ertuğrul dies just before he could announce that Osman is the new Bey.

Osman captures Suci, one of Togay's henchmen. However, Suci is also Cerkutay's blood brother and friend, compelling Cerkutay to save his friend, leading to the tribe believing that Cerkutay is a traitor. Cerkutay, actually serving Osman, later helps the Kayı attack Togay's forces. Meanwhile, a recovered Malhun is sent by her father to İnegöl to ally with Nikola against Togay, although she is captured in the castle by Togay, who has allied with Nikola. Osman also captures Nikola's ally Tekfur Aris, seeking to ally with him, although Togay delivers an ultimatum to surrender the Tekfur in exchange for Malhun.

Osman decides to use Tekfur Aris as bait to trap Nikola. However, Togay kills Aris on the way, providing Nikola with an excuse to keep Malhun in captivity. Nikola also kills Zülfikar Derviş, Osman's spy in İnegöl. Nikola also releases Malhun to gain the support of Ömer Bey, who seeks to sell him horses in order to infiltrate and conquer the castle. The sale of horses angers Osman, who orders them to be seized. Meanwhile, Togay ambushes some of the Kayı on the way back from Boran Alp's unfinished wedding, wounding Gonca Hatun and killing Abdurrahman Gazi.

Osman reconquers Kulucahisar, although İnal Bey is taken by Nikola's knights to İnegöl. Bala and Targun's relations tensen a little and Dündar's evil plans are also revealed, he seeks to become the Bey of the tribe.

As the allied enemies, Nikola, Targun and Petrus continue to stir traps for Osman, Targun ambushes Bala while İdris leads Bamsı into a trap set by Aya Nikola in order to seize the scrolls with Osman's plans for Anatolia. When Osman is alerted, he sets out with half his alps to find Bamsı, only to fall in Nikola's trap and have his tribe pillaged by Targun for the scrolls and a failed attempt by Dündar to become the Bey. Aksu is also killed by Targun before she can confess to Bala about Dündar and Hazal's misdeeds.

Togay, revealed to be Baycu Noyan's son, attacks a meeting of Turkmen Beys chaired by Osman in Söğüt, wounding Ömer Bey. Seeking to sow discord amongst the Turks, Togay frames the Dodurga Bey İvaz Bey for the attack, although his innocence is later revealed. Meanwhile, Lena, having given birth to a son named Ertuğrul, accepts Islam with the help of Şeyh Edebali. Suspecting Dündar's treachery, Osman attempts to set a trap for Dündar and Togay, although Dündar outwits Osman, causing Togay to attack and wound Malhun.

After a series of events including Bala being poisoned by Targun, Targun and Göktug are exiled, which is part of Osman's plans. Dündar has a meeting with Nikola which Osman is aware of resulting his beating when he returns. Petrus' real plans are also revealed, he wants to know what the Turks of Anatolia are planning by seizing some scrolls.

Göktuğ helps Bala defeat Targun in a trap, with Bala eventually killing her. Meanwhile, Osman is saved from Nikola's ambush by Malhun Hatun, a woman requesting Osman for some land for her tribe of 1000. As Malhun settles in the tribe, she questions Osman about his plans. Göktug is made leader of the Cuman Turks, whilst Petrus and Simon demand compensation from Osman for allegedly being attacked. İdris is caught as a spy by Osman, although he is killed by Dündar before he can reveal his treachery.

Möngke's treachery is proven after he is forced to reveal the truth, however, he doesn't manage to say the truth about Arslan thus Arslan survives and Möngke is killed by Geyhatu. In the meantime, Aya Nikola and Flatyos successfully capture Kulucahisar Castle.

Osman Bey confronts the Byzantine-Mongol army with the support of Malhun Hatun. In the ensuing battle, Savcı Bey is stabbed by Kalanoz in the back and dies, which prompts Osman Bey to kill Kalanoz in revenge. Nikola, who gathers troops from the local landlords, plans to raid Umur Bey’s tribe in response to Malhun Hatun's participation, whilst Umur Bey, decides to exile his daughter for fighting against his will. Looking for ways to break the Byzantine-Mongol alliance, Osman Bey agrees to pay taxes to the Mongols, surprising everyone. Togay, who is strengthened by the lands given to his command, plans to turn this situation into an opportunity to consolidate his domination in the region.

Dündar and the Kayı make a trade deal with Tüccar Melik and Süleyman (Simon and Petrus), Ertuğrul comes in Osman's dream reminding him of his will for his second marriage and Nikola is made the "Tekfur of Tekfurs" while his army from Constantinople, led by Alexander, is destroyed by Osman in a great battle. Alexander survives.

After Togay leaves for Konya, his fellow commander Camuha arrives. After Nikola learns Camuha's whereabouts from Dündar, he informs Osman, leading to a successful ambush, although Camuha escapes. Meanwhile, Osman attacks the incoming Kalanoz, younger brother of Kalanoz, after learning of his arrival indirectly from the Mongols, killing many Byzantine soldiers. He invites all Turkmen tribes to join the attack except the Bayındırlı, angering Ömer Bey. Şeyh Edebali later calls Osman and Ömer Bey to Söğüt to resolve their differences, leading to Ömer Bey handing over Dündar's ring to Osman, exposing Dündar as a traitor.

Dündar flees from Söğüt after being exposed as a traitor, and takes refuge with Nikola in İnegöl. The revelation that Dündar is a traitor infuriates Gündüz and Savcı and saddens Aygül. Meanwhile, Petrus and his right-hand man Simon attempt to kill Hazal to cover their tracks, but are stopped by Osman Bey and are captured, with Hazal put under house arrest. Osman sends Gündüz as a messenger to İnegöl and offers a ransom for Dündar, although Nikola declines and demands more gold via Ömer Bey. Eventually, Osman uses Simon to lure Dündar into a trap, capturing him.

After Bamsı Bey's martyrdom, Osman Bey takes an oath to avenge him. Togay, meanwhile, develops an alliance with Nikola and establishes a large army to strike a last blow to the Kayıs. Togay, who enlarges his army with the soldiers he receives from Nikola, stands against Osman Bey and his alps in the battlefield. However, Nikola withdraws from the battle after having a prior agreement with Gündüz Bey, although Governor Yargucu arrives and takes Togay into custody.

The time period given by Geyhatu ends and Geyhatu arrives in Osman's tribe. Osman saves Savcı and he returns to the tribe with the captured Möngke. Ertuğrul continues to stay on his death bed.

Osman is alerted that a distant Cuman Turk tribe has been invaded by the Emperor and the Bey's daughter, Targun, is being taken captive. Osman rescues Targun and takes her to the tribe. However, Targun is betraying Osman, she spies for Aya Nikola to save her father, İnal Bey, who is in Aya Nikola's captive. Hazal also teases Bala that Targun was brought by Osman because he wanted to marry her for a child which she couldn't produce.

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Osman Bey's expulsion of the ambassador who comes to the tribe to receive the tax causes Togay to break his truce. This causes the Seljuk Sultan, Mesud II, to summon Osman Bey to Konya to punish him in order to protect him from the wrath of the Mongols. Learning that Osman Bey refused to pay taxes to the Mongols from a spy in the tribe, Nikola takes action to increase his influence by taking advantage of the Mongol-Turkish war. Bamsı Bey also kills Petrus after Osman realises Simon was killed by Nikola. Cerkutay, on the other hand, becomes a Muslim under the witness of Sheikh Edebali. Umur Bey develops a plan to attack Togay, which is opposed by Osman. After a confrontation between the pair, Sheikh Edebalı tells Osman Bey that he must marry Malhun Hatun in order to gain the support of Umur Bey and achieve the goal of uniting the Turkish tribes.