Usually, I hate one-off episodes but this one I loved. I think it was a delightful tale of the two people that the writers haphazardly threw into the storyline. I was very crafty and creative how they were able to weave two strangers into this three season journey. They did a damned fine job.
It was great to see Billy D. Williams. That old man still has it. :)
It was a tale of Nikki and Paulo, two con artists who killed a movie director for his diamonds. They were on the plane and crashed with everyone else. They've been living under the radar but with everyone else this whole time. When they crash, they loose the diamonds. Paulo eventually finds the diamonds but doesn't tell Nikki. Nikki finds out and uses a spider that paralyzes to get the gems from Paulo. They both end up getting bit by the spider and get paralyzed. Everyone thinks that they are dead and the two end up being buried alive with the diamonds.
So tragic and awful but still awesome.
More at the Lostpedia.