Way to unlock: You need to complete Main mission 10 (Friend Request). Wait for a phone call from Amanda, answer the phone and listen to the conversation.
Playable characters: Michael
Additional information: It is a very unique mission in that it is not compulsory and the game does not take it into account while determining your progress with the main missions. It only consists of a three-star police pursuit and, because it is Michael that takes part in the chase, instead of Franklin, losing the enforcers is not going to be that easy.
Some time after the completion of the tenth main mission,, while playing as Michael, you should receive a phone call from Amanda who is asking for help. Towards the end of the conversation, you will have to decide whether you want to help her or not and it is obviously better to go for the former.
The game will start a timer but, you should have plenty of it to reach the Rockford Hills district (as the last resort, you should try to find a fast car). After you get there, get into the squad car (Police Cruiser) with the arrested Amanda in it, which will start the chase (3 stars).
Just like in the case of pursuits in the previous missions, try to make use of side-roads to lose the cops. Since there is also a police chopper involved, try to hide in the place where you will not be detected from aboard the helicopter. Wait for the police to give up further search and take Amanda back home.
Rewards for the completion of the mission: none
Requirements for the completion of the mission in 100%: There are no additional requirements to this mission so, it is completed in 100% automatically.