Trama

A man enters a machine called the Animus that lets him relive the memories of his ancestor, a 12th century assassin named Altair.

The saga begins when Desmond Miles (Nolan North), a bartender, wakes up suddenly from within a strange machine inside an upper level laboratory. He angrily confronts the man responsible for bringing him there, Dr. Warren Vidic (Phil Proctor) of Abstergo Industries. Vidic tells Desmond that he knows who he truly is, an assassin, and that he'd better do what he tells him to do. Desmond tries to explain that he is no longer an assassin but Vidic doesn't care. What he does care about is information that is stored in Desmond's head. Vidic explains to Desmond that the machine he was in, the Animus, is designed to hack into a person's subconscious and play back 'genetic memories' so that the subject is able to re-live the lives of his ancestors. In Desmond's case, they are trying to collect information about his ancestor Altaïr ibn-La'Ahad (Philip Shahbaz), an assassin who lived during the era of the Third Crusade in the tenth century. Begrudgingly, Desmond agrees to follow Vidic's commands seeing as he has no other choice.

Altaïr's story begins during a mission into a secret temple. As he and his two subordinates, Malik A'Sayf (Haaz Sleiman) and his brother Kadar, sneak into one of the passageways they come upon a gathering of Templars, centuries' old enemies whose forceful methods of global peace involve domination and control. Robert De Sablé (Jean-Philippe Dandenaud), the Grand Master of the Templar Order, is attempting to haul off a treasure that the assassins were sent to claim. The proud Altaïr manages to break all three of the Assassin's Tenets during the subsequent encounter: he kills an innocent mine worker on the way to the treasure room, he makes his presence known to his enemies, and he comprimises the Brotherhood by failing to kill Robert and being thrown out of the room while Malik and Kadar are presumably killed. Altaïr makes his way out of the temple and returns to the Assassin stronghold, Masyaf, where he presents himself empty-handed to his mentor, Al Mualim (Peter Renaday). However, shortly after Altaïr's arrival, Malik returns to Masyaf without his brother but with the treasure Al Mualim sought; a delicate, gold orb. Malik is injured, his left arm maimed, and bears an unyielding hatred towards Altaïr for being the cause of it all. Al Mualim reciprocates Malik's judgements on Altaïr's character and summons the latter to death for his arrogance.

However, Altaïr is spared this fate by Al Mualim, instead demoted to the rank of Novice, and has most of his weapons taken from him. Altaïr is tasked with assassinating nine members of the Templar organization, all powerful leaders in various cities throughout the Middle East, in order to redeem his former status. Altaïr travels between the ancient cities of Jerusalem, Damascus, and Acre, killing each of the leaders in sequence and performing side tasks along the way. Upon arriving in each city, Altaïr must first make contact with the Brotherhood's bureau leaders; Malik, reassigned to Jerusalem because of his injuries, Jabal in Acre, and Rafiq in Damascus. Each leader instructs Altaïr to collect data on each of his targets before striking and request that he return to them with proof of each successful mission. Each success also requires a trip back to Masyaf where Altaïr is given his rank and weapons back bit by bit along with new information from Al Mualim.

Among the Templars are Tamir (Ammar Daraiseh), a Saracen black market merchant in Damascus, Garnier De Naplouse (Hubert Fielden), Grand Master of the Knights Hospitalier in Acre, Talal (Jake Eberle), a Saracen slave trader in Jerusalem, Abu'l Nuqoud (Fred Tatasciore), the Merchant King of Damascus, William of Montferrat (Harry Standjofski), an Italian Crusader and King Richard the Lionheart's regent in Acre, Majd Addin (Richard Cansino), Saladin's regent in Jerusalem, Sibrand (Arthur Holden), a German Crusader and the first Grand Master of the Knights Teutonic in Acre, and, of course, Robert de Sablé, lieutenant under King Richard.

As Altaïr kills each of them in sequence, each man maintains his justifications in the atrocities he's committed, giving Altaïr doubt in his own actions and the Brotherhood itself. However, his doubts are trumped by assurances from Al Mualim who gives him fatherly advice and praises each successful mission.

Meanwhile, in between trials within the Animus, Desmond is allowed to rest and explore the lab. While Vidic is both impatient and gruff, his assistant, Lucy Stillman (Kristen Bell), is of a gentler nature and does her best to explain her role in everything in addition to what is required of Desmond. She and Desmond bond over time and she eventually confides in him that, while Vidic is often harsh, she owes him her life. When a few Abstergo agents attempted to assault and kill her shortly after she was hired, Vidic was the one to call them off. That, along with the ability to advance her career, gave Lucy the motivation to continue her work in Abstergo despite knowing that the conglomerate is completely staffed by modern Templars. Desmond figures out that the treasure recovered by Al Mualim is what the Templars are after, an artifact known as a 'Piece of Eden'. While Desmond continues to re-live Altaïr's life, he begins to experience what Lucy calls the 'Bleeding Effect', a sort of programming of Desmond's brain that gives him all the abilities and traits of his ancestor. One of these traits is something Desmond's had since birth, called 'Eagle Vision'. This sixth sense allows Desmond, as it did Altaïr and others within his lineage, to immediately detect various targets, enemies, and their locations. The downside to the Bleeding Effect is that Desmond begins to suffer mild hallucinations, blurring the line between past and present. Lucy warns Desmond to keep his mind about him, mentioning that the last subject, dubbed Sixteen, was kept in the Animus so long that his mind deteriorated to the point where he could no longer distinguish realities and wound up killing himself.

Altaïr's last target is Robert de Sablé himself. Altaïr tracks Robert to Acre where his attempt to assassinate him reveals that Robert enlisted the use of a double in his stead. The female Templar, Maria (Eleanor Noble), is left alive by Altaïr since she is not his target. He finds the real Robert out on the battlefields with King Richard (Marcel Jeannin) and openly accuses him of treachery in front of the King. King Richard proposes that God decide who is telling the truth by allowing Altaïr and Robert to fight to the death. Altaïr proves victorious and, with his dying breath, Robert reveals the existence of a tenth Templar; none other than Al Mualim himself. Robert claims that is the reason Al Mualim knew so much about the other Templars and where to find them. He killed them all with the intent of keeping the Piece of Eden to himself and will now surely kill Altaïr for knowing too much.

Altaïr returns to Masyaf to find its citizens and his fellow assassins under a spell with only a few strong enough to resist it. With Malik and a few loyal assassins at his side, Altaïr confronts Al Mualim who is revealed to be using the Piece of Eden to control people's minds. Altaïr fights Al Mualim one-on-one, seeing through his trickery, and kills him. He vows to destroy the Piece of Eden but, as he approaches it, a projection is activated by his presence and a map of the entire world is displayed, marking several key spots around the globe.

At this point, Desmond is brought out of the Animus to see Vidic addressing a board of superiors on his findings. His purpose served, Desmond is ordered to be terminated but Lucy steps in, telling Vidic that they may need Desmond in the future should something go awry in their plans. Vidic leaves the room and, before she follows, Lucy reveals to Desmond that she is actually an assassin mole and his ally by bending her ring finger back; the significance being a reference to the absence of a ring finger on Altaïr's left hand in order to allow a path for his hidden blade weapon. Alone, Desmond suddenly begins to experience a Bleeding Effect, seeing the room in Eagle Vision mapped with strange symbols. In his room, he discovers a tapestry of symbols and coding drawn out in blood on the wall; the last message of Subject 16.