Way to unlock: You need to complete main missions 66 (Getaway Vehicle #2) and 67 (Fire Truck), and contact Lester. You may now return to the clothes factory, i.e. Lester's base (letter H on the world map).
Playable characters: Michael, Franklin
Additional information: The initial part of this mission is very calm because Michael will need to take on the janitor's duties and plant the explosives while cleaning the floors. The second part of this mission is more interesting, because it assumes infiltrating the building under the guise of firemen. Do not expect that the workers of the Agency will remain oblivious to your actual plans until the very end, but still, you will need to eliminate only a small group of agents, and only after you steal the data from the server room.
You start off as Michael. Exit the clothes factory, get into Michael's car (Obey Tailgater) and drive to the Pillbox Hill district, i.e. to the FIB skyscraper. Park in front of the building, walk inside, around the security gate and walk into the elevator. Enter the maintenance room and wait for Michael to collect the mop.
Walk towards the first part of the offices. Put the bucket down and start removing grime from the floor so, approach the red dots on the radar and press the correct button. Each time after you remove stains, return to the bucket to clear the mop. After you have performed all of the work in this part of the building, approach the boxes, thanks to which Michael will automatically place a bomb there.
Walk into the next part of the office floor. Here, there are four different fragments of the floor to clean so, get busy. Remove the stains from the first two fragments and go, with the bucket, to the next corridor. After you are done with your cleaning job, enter the men's restroom and wait until this area is left by one of the employees. You can now enter the stall marked by the game and plant the second bomb there.
Pick up the bucket and return with it to the maintenance, at which you have started the exploration of this floor. Take the elevator down and exit the skyscraper. Stop in the marked area and wait until you cut to Franklin. Approach the spot where you are supposed to take Michael aboard the fire truck and select your smartphone from your inventory. Access the Contacts list and confirm the detonation of the explosives (the above screenshot).
You can now drive towards the FIB skyscraper. In accordance with the information, you can take your time because the other units did not receive the notification, as a result of Lester's actions. Park in front of the skyscraper and get inside. Use the elevator again to reach the 47th floor. Starting here, it is a good idea to perform all of the actions in a hurry because your oxygen supply is limited, which can be seen on the bar in the bottom-right corner o your screen. Oxygen will be depleting very slowly, but do not be influenced by that, as there are many actions to perform. Your current objective is to get to floor 53 so, follow your teammates to reach the staircase.
After you have reached floor 53, start crossing one office after another, towards the server room marked on the radar. From the inventory, select the sticky bomb, aim at the server room's door (the above screenshot) and detonate the explosive from afar. You can now enter the server room and collect the disk with the data.
Exit the server room and start going in the opposite direction, by following Michael and the rest of the team. Things will get complicated after you reach the staircase, because it will turn out to be destroyed. This means that you need to cut through floor 52. After you experience a small explosion, help your teammate up and resume your run across the demolished building. Make use of a structural element to reach the lower floor.
Franklin will soon be temporarily incapacitated. After you regain full control over him, set out to meet up with your teammates. You can take your time because you will have to handle the first wave of hostile Agency workers. Fortunately, the enemies are not too well armed so, try not to lose too much time while attempting to eliminate them. Keep cutting through successive offices in the building and attack the enemies that will be coming in groups of two, at most. Ultimately, you need to make it to the staircase and climb down to floor 50.
Soon after you start the exploration of floor 50, you will meet the remaining characters again so, continue following them. Reach the elevator shaft and, after you see a short cutscene, abseil down the sling. While playing this part, it is a good idea to bounce off the shaft's walls on a regular basis and perform long jumps which will speed up the whole process. Also, ignore the big elements falling down, because none of the should hit you anyways. After you reach the ground floor, dash out of the building and get into the fire truck.
You can now return to the spot where you have left the getaway car, while completing one of the previous missions. As long as you have chosen a spot close to the FIB skyscraper, you do not need to worry about the police pursuit. After you get to the car, destroy the fire truck (e.g. using another bomb), get into the car and wait for the rest of the team to join you. The only thing left for you to do now is safely reach Lester's home located in the El Burro Heights district.
Rewards for the completion of the mission:
- Receiving of cash for the FIB headquarters' heist (your pay depends on the pay of the two hired members; only Franklin will receive his pay)
- Skills of the hired members increased (if they survived)
Requirements for the completion of the mission in 100%:
- Time - You need to complete this mission within 18 minutes. Try not to lose too much time "playing the janitor" and during the fights towards the end of the mission. It is also a good idea to have the car parked somewhere near the FIB skyscraper.
- Out of Breath - While leaving the FIB skyscraper, you need to have, at least, 40$ spare oxygen. This, of course means, that you cannot allow yourself to take stops too often, while exploring the building dressed up as a fireman.
- You Missed a Spot - You need to perform all of the janitor's duties within 3 minutes. Clean the mop on a regular basis and do not stop on your way towards the consecutive areas with stains.
- Abseiler - You need to zip down the elevator shaft within 30 seconds. This is easy to achieve only if you regularly bounce off the walls, which speeds up the way down.