After the Arena, this is all but literally a walk in the park. Join Idril in a midnight stroll down to the orcish camp. Like Baranor, Idril can be sent to attack guards on your order, and she makes her stealth check with surprising regularity.
Sneak-kill the first two orcs. These are last ones that you *have* to sneak kill- while your game here is rescuing hostages (you can free them with L+CTRL, or Idril will free them if left to her own devices), alerting the orcs won't enrage them into killing captives.
With those first few soldiers free, you can now move into the camp proper. Wraith vision will show enemy distribution in red (as per usual) and the hostages in yellow.
You can play this as you like- stealth is a little more fun, but you're going to end up killing all these guards anyway, so don't stress about raising the alarm. Still, shadow-striking the archers up high is good part of any plan.
When all hostages are clear, you'll get an objective to wipe out the remaining guards (if there are any remaining guards). After that, follow your marker to rescue Castamir (in cutscene).
You'll now retrace your path from the very beginning of the game- up the road and across the bridge. You can dispatch both Idril and her dad as stealth killers, but it's scarcely necessary- everyone between you and the gate is a non-name pushover. Return to the upper city to complete the mission.
