I got the Rescue Mission for Vilkas of the Companions, and was instructed to save Amren from Broken Fang Cave. I go to where the quest marker is and find myself in the middle of a dry lake, just west of Whiterun, with mudcrabs. No cave. I look around on the map, and find Broken Fang Cave quite a ways south west of where I am. I go to the cave, kill the mobs within, but no Amren. I check the quest and it shows "rescue completed" and the next step as "talk to Amren". I also note that the quest marker is again on the dry lake from before. So back to the lake I go, knowing that the quest is bugged. Of course, Amren is not there. I use the console to go to the quest marker. Next thing I know I'm falling from the sky and splatting on the ground, with Amren splatting soon afterwards. I reload from a previous point with the same end effect. I activate God Mode, then retry. This time we both survive. I figure, no big deal, as long as I can complete it. It's off to Whiterun we go. We enter the city and the quest marker is on the ground just inside the gate. Amren won't trigger no matter how many times I run over the marker. He keeps saying "please take me home". Fine, we go to his house. Nothing. Reload, try again; same thing. Now I have Amren following me around and no way to finish the quest. I take him to the Moon Camp and subsequently drive my sword through his heart. QUEST FAILED. As anol as I am, and although I am level 20, I'm about to start over because of this.

I did a similar quest but everything worked right. Well except I'm not too sure how much my companion needed rescuing. I got into the cave, killed one chick in the front and was told he had been rescued. Went to the back and there were about 4 dead dudes around him and he was waiting for me...