This episode is if not my all time favorite one of them. After Venger closes the portal back to Earth right as the group is about to step through they decide enough is enough.
After Dungeon Master does his usual vague hinting at how to find Tiamat, the group puts it together and their magical items transport them to the Dragon's Graveyard. Using a horn of summoning Tiamat is called and agrees to bring Venger to them, since in the Dragon's Graveyard their magical items are much more powerful.
Once Venger arrives he is defeated and ultimately Hank decides not to kill him. He instead releases Venger. Venger is very vexed by this asking why. Also Dungeon Master when he goes to Venger says "Rise, my son." So the hints about who Venger is are there.
This episode, as the entire series, is about doing what is right. The group, and Hank inparticular, in due course come to the right decision. As Hank states "If I did (finish Venger)we'd be no better than you are." This is the heart of the entire series summed up.