Bruz is up to no good, having kidnapped some of your orcs and poisoned them, with incredibly slow-acting poison. Given the orcish reputation for flaying, fleshrending, and marrow-guzzling, this seems positively quaint. Follow Ratbag to the scene of the crime
Freeing your captive soldiers is just like freeing Gondorians, and the rank insignia make them even easier to find.
Your optional objective here is to defeat enemies with Shadow Strike, but it's no hardship- Shadow Strike is one of the bet way to navigate the weird architecture here anyway. You can get an even farther range by pairing it with a sprinting leap and Bird of Prey
When the last captive is freed, you face Bruz' follower, a highish level captain.
The space here is tight, but it also means enemies have trouble ganging up on you, even if they can pathfind their way over. Use stuns, freezes, and pins to keep your foe cornered, and then knock him into submission.
Ending his scheme ends the mission.