This adventure took place in my friend's realm and used Dungeons and Dragons, Second Edition rules. Our party consisted of three player characters and one NPC. My character was a female half-elf ranger; the other two player characters were a minotaur fighter/mage and a large furry druid of a species I can't remember the name of. The NPC was a drow that we ran into along the way.
After getting together, we ended up in a small village, where we discovered that a kid had wandered into nearby ruins. Except for the drow, we were of good alignment, and so we decided to go out and find the foolish kid. He was in a tomb that was in these ruins, where we discovered an ancient sarcophagus marked with the glowing seal of a long-dead civilization. We also encountered a necromancer here who was controlling a skeleton warrior using a circlet containing the warrior's soul. We began to fight the skeleton warrior, assuming that whatever the necromancer was here for was something we wanted to prevent.
During the fight, the seal on the sacrophagus was damaged, but the minotaur managed to kill the necromancer. With this, the skeleton warrior was freed. He immediately retrieved the circlet containing his soul and broke it, allowing himself to finally die. Unfortunately, the necromancer had still completed his mission; the damage to the seal of the sacrophagus weakened the magic holding its occupant inside. We were about to discover that this sacrophagus held Lord Drakmare, a death knight (extremely powerful undead warrior) and the commander of the Nockmare, an army of undead serving the evil goddess Moragon.
Lord Drakmare split the sacrophagus in half and emerged without his armor. One of the abilities of a death knight is a natural fear aura, and every one of us failed our saving throws vs. fear. As a result, each of us froze up. We were defenseless before the most powerful death knight in the entire realm.
Fortunately for us, Lord Drakmare was a little too happy to be free after a thousand years of imprisonment to bother with us, and so he simply left instead of killing us for our impudence. After breathing a massive sigh of relief, we set out back to the village with the kid in tow. Lord Drakmare destroyed the village on his way out of the area, unfortunately. Naturally, we were blamed for releasing him; no one believed our story that we had tried to prevent this. Thus, for our good deed, our reward was the enmity of the survivors of this village, and we were forced to leave.
This would not be our first encounter with Lord Drakmare, however. Later, we would get a chance to repair our reputations and remove Lord Drakmare's threat, at least for a while, but it wasn't difficult to forget how we failed to stop his escape.