Into the Storm is the second main task available in Assassin's Creed Odyssey: Legacy of the First Blade.
This mission consists in entering the enemy fort and the releasing a group of four prisoners.
Two prisoners are in one square. To get to them, kill the guards first in this part of the camp. If you don't do this, they will call the rest of the security.
It's best if you move quietly through the fort. Kill in stealth mode and disturb enemies. This way you will avoid a direct fight with a large group of people. This will speed up your mission considerably.
After you've released the prisoners, go to Darius and talk to him. This will complete the mission of Into the Storm.