刺客信条：秘密圣战（Assassin's Creed: The Secret Crusade）是根据刺客信条系列游戏改编的第三部小说。本书由奥利弗·波登撰写，企鹅出版社出版发行。
Altaïr decided to follow Shalim, in hope to find Maria, but instead, ending up at a brothel, so he returned to the market place where Markos was. He told Altaïr that Shalim had to go to the cathedral a lot, since he needed to make frequent confessions about his lifestyle, and that he thus had to speak to the monks there, to find out more about his target. There he found Shalim himself, speaking about Bouchart's wishes to the crowd he had gathered. Shalim left, Altaïr followed, ending up at the St Hilarion Castle, in which Shalim disappeared. The Assassin, having lost his target, sat down on a low wall nearby as some courtesans crossed the docks, Maria being one of them. With them, he entered the castle, unnoticed.
Altaïr did not know Shalim had a twin brother, Shahar, and that he was the one delivering the speech. Maria and Shahar conversed about the Templar ways, before being interrupted by Altaïr. The real Shalim came in with guards, and the Assassin finally noticed they were twins. Maria quickly disposed of the guards, then fled, leaving Altaïr to fight two skilled swordsmen alone - slaying them both. Later, he returned to the safe-house, telling Markos he would be heading back to Limassol. He also wrote another piece of the Codex, page one.
Arriving at Limassol, he located the safe-house and found Alexander. In a brief confrontation with him, Altaïr found out that he wasn't a Templar, but the two had been set up against each other, as they were both tricked into believing each other were Templar-sided Resistance members. Altaïr then headed off to a failed search for Bouchart, coming back to find the safe-house empty, a note left there for him. The Assassin went to the courtyard where the note said they were due to meet, only to find the dead body of Alexander; it was a trap. The fake Barnabas came out, and as Altaïr unsheathed his sword, he opened the door to the resentful crowd outside, to make them think the Assassin was the one who killed Alexander. Altaïr couldn't kill civilians, so he used the Apple he had with him to persuade them to his will, saving himself and setting them up against the Templars. 'Barnabas', prepared to fight, came down the ramparts. However, he was stopped by Maria, who put a blade through his chest.
Maria then took Altaïr with her to the Archives, telling him to follow her, being obstructed by guards on his path, but eventually making it into the almost empty library, seeing both Bouchart and Maria. She was holding off the Templar leader, only just, before being struck by his sword, tumbling, yelling in pain. Bouchart made the first move, quickly tiring, and Altaïr made the last, the dying man giving him respect - and ignorance - for this, telling the Assassin of the power of the Pieces of Eden as he drew his last breath. Cannons were then fired at the Archive, to destroy every last piece of it. Altaïr quickly escaped, taking Maria with him. Later, after the Templars had left, taking all the pieces of archive with them, Altaïr and Maria were talking to each other again; Maria telling Altaïr she was heading east, at which he replied he was also heading east.
Niccolò told Maffeo that Darim, who invited them to Masyaf, was the son of Maria and Altaïr. He explained that Maria and Altaïr were wed in Limassol, and that Maria gave birth to a second son two years after Darim was born; Sef. He also told him that the Codex was a summary of all the discoveries Altaïr had made, and he tried thinking of why they were invited in the first place; maybe because it had to do with them living in Constantinople? He then continued the story at the point Altaïr returned from his travel East, to a Masyaf where everything had changed.
The Ibn-La'Ahad family rode slowly into Masyaf, where Swami - still an apprentice when Altaïr left - greeted them first. Masyaf had become a darker place, and had changed much to what Altaïr had planned it to be, acting in on the Assassin's instincts. They were led to a small house to the west of the fortress, where they were told that Malik was in prison, Sef had traveled to Alamut, and a meeting of the council had been planned the next day; with Abbas as chairman. Altaïr told Darim to ride to Alamut, in order to bring Sef back.
The following day, Altaïr and Maria were led through the citadel by Swami, to the council, where Altaïr was forced to report about his trip to the East. After the story, Abbas informed Altaïr and Maria that Sef had been killed by Malik, which was why he was imprisoned. Then, as Altaïr lost control of his emotions, he stated that the former Mentor could not resume leadership of the Order, thus the leadership stayed with the council.
Back in the small cabin, Maria and Altaïr discussed their situation; Masyaf had been neglected, Sef who had been murdered by Malik, Abbas who was now leader of the Order and the Apple that Maria wanted to be destroyed by now. Altaïr headed for Masyaf's dungeons, where Malik laid, neglected and emaciated. There, Altaïr found that he wasn't the one who murdered Sef.
He took Malik back to the cabin where both Maria and Altaïr cared for the almost dying friend. Malik told them Sef had been murdered by Abbas as he staged his coup, two years ago. In the next room, Altaïr and Maria planned their next move; to confront Abbas. Moments later, Altaïr stood at the courtyard with Abbas, who had his Assassin loyalists gathered with him. There, Swami came up to Abbas, delivering a sack to him. What Abbas pulled out of that sack was the head of Altaïr's former friend, Malik, eyeballs rolled up and the neck dripping with fresh blood. Abbas accused Altaïr of murdering Malik, then took Maria and held a dagger to her throat - the same dagger his father had killed himself with. Altaïr then pulled the Apple from his robe, which Swami instantly reached for. All of Altaïr's rage was transmitted into Swami, as he brutally - controlled by the Apple - killed himself with his own hands, then he took out his dagger and slashed himself open. Maria, trying to reach for Altaïr, was hit by Swami's dagger at her throat, both of them falling to the ground, dying. As Abbas ordered his loyalists to kill Altaïr, the Assassin fled. He finally reached the top of the tower of which he had jumped a lifetime ago, he hobbled to the platform, spread his arms out, and dropped.
Niccolò finally understood why he had been invited: to spread the word of the Assassins. Maffeo now wanted to stay, while Niccolò wanted to leave, whereas it was vice versa at the beginning of their stay; the reason being that Mongols were heading to Masyaf. Niccolò told the reader he had had some presents from Altaïr, having his suspicions as to what they might be. He skipped the story to a man in the desert, twenty years from where Altaïr escaped from Masyaf. ... Mukhlis, a tradesman, was on a journey back to his family in Masyaf; now he was somewhere in the desert, a two days' ride away from home. He had heard of bandits plundering throughout the desert, taking all belongings and leaving the owners upside down in trees with their guts hanging from them. Bayhas, son of Fahad, being the most brutal of all. Mukhlis was forced to rest, and the next day he found himself with a stranger hanging over him, holding a blade to his neck. He and his companion bandits hung him in a tree, but before they could kill him, Altaïr arrived.
The old Assassin instantly took out one of the three men. A battle started and Altaïr, outnumbered and not in the best shape, was immediately tired out, bleeding severely from his wounds. There, Mukhlis - still tied hanging to the tree - grabbed hold of Bayhas, the leader of the bandit group, at which Altaïr sliced the enemy open in his last strand of power, scaring off the third bandit. Then, Altaïr went unconscious almost bleeding to death. Mukhlis, having freed himself, put Altaïr over his horse and headed home.
One of Fahad's men had claimed the life of Bayhas' killer, and word had spread about the return of Altaïr throughout the village in the week the Assassin had been unconscious. As he awoke, he spoke to Mukhlis about his current situation and where he had been after throwing himself off the tower, also mentioning how he was planning to free the village.
The next day, Altaïr intervened in fights, showing the people of the village the Assassins' ways. He also went to the basket-weaver and a blacksmith to get his weapons made; all ideas taken from the Apple. The next few days Altaïr noticed a man watching him, stalking him. He eventually showed himself, turning out not to be an enemy but a friend. It was Malik, son of Malik, known as Tazim to most of the Order. He let Altaïr know that he and some other Assassins would join him in taking back Masyaf.
The day after, Mukhlis informed people of the village that the Master was to march up the hill, which excited them into gathering at the marketplace, where Altaïr then joined them. He thought of what had gone through him, what Maria would've said if she was still with him. There, at the marketplace, Altaïr and the villagers waited for young Malik to come back with his support. After some time, men dressed in white robes with cowls came from the shadows, to immediately win the trust of their leader who had doubted Malik's stealth. Immediately they left for the hills, to Abbas, with the instructions not to kill anyone. There, marching toward the fortress, Abbas' loyalists attacked, to soon be neutralized, unharmed. Above, where Abbas' archers were, this sparked a rebellion, unwilling to shoot their own people, following the example Altaïr had given. Inside the castle, Altaïr and Abbas faced each other, Abbas still accusing the other of lying about his father. Then, when Abbas ordered his men to kill him, Altaïr shot him with his newly acquired Hidden Gun, scaring off any of the enemy's followers. Abbas shared his last words with Altaïr, where the old Assassin still saw that orphan boy the moment he passed away. Two days later, Fahad came back to Masyaf, explaining that it was mostly his wife's interference that he had to avenge their son's name. Fahad left, in good mood, thanks to Altaïr's negotiation skills.
Niccolò described how the Mongols had arrived, and that Altaïr had gathered with them to give them their last objects to keep safe; artifacts - five of them, each of them being a stone with a hole in its center, keys imbued with a message. Then Niccolò and Maffeo left Masyaf, which was already being overrun by the Mongols, Altaïr barking orders at his Assassins to try and fend off their enemy.
The Polos had lost the Codex, but were still holding on to the artifacts. They decided to hide them in Constantinople for an Assassin of the future to find. They also spread word of the Creed and set up an Assassins guild there, in Costantinople.
The mysterious Assassin - the reader - heard noises from his cabin, indicating they were approaching land. He closed Niccolò's journal, secured his blade mechanism and pulled up his cowl. From there, he opened the hatch of his quarters to see people welcoming him. Ezio was in the great city of Constantinople.
- All Memory Corridor dialogues took place in the book, but they were explained either by the stealthy assassination of a target or through the guards being shocked and allowing the scene to play out.
- After being demoted, Altaïr began his quest for redemption by immediately going to Damascus in order to kill Tamir, skipping the hunt for the traitor in Masyaf entirely.
- Altaïr did not interact with informants during his investigations of the nine targets.
- Altaïr witnessed the rescue of the captured Assassin after Majd Addin's assassination.
- It was hinted that, in the book, Altaïr still retained his ring finger and that it was used to trigger the Hidden Blade's mechanism.
- Altaïr assassinated Jubair in the Madrasah, whereas in the game he had to track him down among his followers using Eagle Vision.
- No mention was made of Altaïr advancing through the ranks of the Order after each assassination.
- Altaïr assassinated Abu'l Nuquod on the balcony of his palace, whereas in the game he had to chase him down, although it is possible to kill Abu'l Nuquod on the balcony if he is grabbed in time and thrown towards it.