The only thing of note in the secret passage that you may have missed is a skill book, in a hidden room just past the door Martis unlocks during his escape. Through the door...
the main path turns left; straight ahead is a short passage partly covered by a spider web, past which is a pressure plate on the left wall.
In the original release of D2:ED I mindread Martis in jail, but did not turn in the quest by telling Louis what I learned. This resulted in Martis being broken out of jail by a couple bandits as I got there, and there was no cave-in. In DKS I skipped that mindread and broke him out myself, but there was no cave-in for me that way either (not sure what triggers or avoids the cave-in in that case).
If you have not done so already, visit the bandit camp yourself before telling Louis the location and password (there are a couple quests there, and Martis is a decent merchant; I didn't check him every level, being out of the way, but got a few pieces of equipment from him with enchantment upgrades).
Welcome to the forum.
Well .. er .. she's arrived in Aleroth after the battle in Ygerna's Memory ... but in some way I'm afraid to play further on that part ? Why ? Because Flames of Vengeance is very addictive part for me and this year 2012 I haven't the time to play that much ! 
... 