In the Belly of the Beast is a main mission under Albion in Watch Dogs: Legion.
Your task is to enter TIDIS and shut down project THEMIS with microdrones.
Here’s a walkthrough of In The Belly Of The Beast in Watch Dogs Legion.
Search for project THEMIS
Head to Southwark at the location provided in the map.
You can enter the Tidis building through the main entrance but you don’t need to get through the alarm door.
At the left side, there’s a vent for a spiderbot. Use a spiderbot and crawl in.
Keep going until you reach a locked door. There’s another vent at the side of the door.
Go through the vent and you’ll be inside. You might want to takedown some of the officers.
The captain holds the key. Download the key from him.
You’ll then find a locked door upstairs but if you’ve downloaded the key, you can enter.
Access the vault
You’ll then be required to access the vault downstairs. Get back to your character and enter through the front door, after disabling the alarm.
The elevator to the vault is locked.
Use a spiderbot and crawl through the vent beside the elevator. Enter the vent and unlock the elevator from the inside.
Use the elevator and go down.
Deploy the microdrone
To get to the microdrone, you need a spiderbot. Use a spiderbot and enter the vent.
After the vent, jump up and look for the next vent.
Follow the route until you reach the laser part.
You have to get through the laser. You just need to time your movement. For those three parallel lasers, you can jump over all of them.
After the lasers, enter the vent at the left.
Inside the room, interact with the device to deploy microdrones.
Destroy the power grid
You then need to destroy the power grid, but this part can be long.
Fly towards the end and you’ll see a locked vent. Use the lasers to shoot the two locks holding the vent.
At the wind area filled with electrical walls, go to the right side and fly low.
If you come across heated parts after this, you can actually disable them. Just use the lasers to shoot at the cores and the heat will stop for some time.
You will then have time to fly through the hot parts.
Keep going until you reach another windy area with electrical walls. Use the walls to hide behind the wind and basically just avoid the wind.
Keep going until you unlock the next checkpoint.
At this part with winds and electrical walls (image below), you need to fly low following the cables all the way.
You’ll get to avoid being blown away.
You will come across another area where the wind blows directly at you. Just follow and use the cables to block the wind.
Keep going until you reach another heated area. Get past the area and you’ll reach the power grid.
Shoot at all the power grids (light brown) in this room and your job here is done.
Access the THEMIS files
You’ll be controlling your operative again. Get to the end room to access the THEMIS files.
Erase the THEMIS files after the presentation.
Leave the area safely to complete the mission.