After completing all the main missions and contracts, you will come across the second last quest of AC Mirage, The Last Journey. After assassinating Qabiha, you must escape the palace and meet Nehal in the hideout. You will discuss the information Qabiha mentioned. She will tell Basim about where he can learn the truth about himself.
To do so, it is time to meet Nehal and head to Alamut.
Escape the Palace
After you have completed the Serpent’s Nest mission and assassinated Qabiha, the second last quest of AC Mirage, The Last Journey, will begin. It triggers immediately after the assassination when the palace is highly alert, and you must now escape.
Take the only route out of the bathhouse, and you will find a group of guards. There is no choice here but to fight your way out. The best way to deal with them is to parry them and then kill them using the prompt on the screen. Once they are all dead, turn left to the long stairs.
Proceed forward and turn left near the end. Sprint forward and take the stairs to your left to reach the level above the throne room. Jump down to the throne room and proceed forward. Out there, you will get ambushed by four guards and four marksmen.
The marksmen will be shooting arrows at you even if you are fighting the guards. It is wise to ignore everyone and flee the palace through the main entrance. Once you are far from the palace and you lose the guards, the objective will change to Meet Nehal at the hideout.
Meet Nehal at the hideout

Fast-travel to the nearest viewpoint near the hideout and cover the rest of the distance to reach Basim’s old house in Anbar.
After you enter the house, a long cutscene will trigger. In this cutscene, Basim tells Nehal about the truth that Qabiha tried to tell him. But Roshan would have murdered her before she could say anything. He will further mention that the truth lies in Alamut. Listening to this, Nehal will ask you to ride to Alamut together.
Since this is the second last mission, you will not be able to return to Baghdad before completing the final quest. If you have any upgrades you need to get, select the Not Yet option and head out. Once you have prepared to take on the last mission, return to the same place and accept Nehal’s request to head on to Alamut.
This marks the end of The Last Journey in AC Mirage. You will return to Baghdad after the final mission to free-roam and finish anything you left off.