For a one-shot my group really liked the "Worse Than Death" adventure in Dungeon by Robert Schwalb. It is good if you want a mix of role playing, fairly fluid skill challenges and fights with a bit of creepiness. If you want straight sequential combat it might be best to pass on it. If you are not a DDI subscriber ignore the rest of this post.
The best part of the adventure is that is allows for alot of on-topic, focused roleplaying. The key is to read up on each of NPC and try to play them as real people. Imagine you are in a TV procedural like CSI or Bones. I introduced a couple of servants in the beginning to plant a seed in the player's minds. Basically, I tried to pass off Festaud as a decadent playboy way over his head.
I skipped the "tracking the kidnappers" mostly because I find these kind of "getting from A to B" challenges a waste of everyone's time. I quickly had them make some checks just to keep people on their toes and moved on. In your case, since you won't have time for a second session, I would skip it entirely or fake it and have them make a few checks. If they do well reward them with the Night Knives fight. If they roll poorly then punish them with the Night Knives fight. Let your chops as a DM set the tone.
The "crime scene" is fun because you can drop a lot of red herrings. I had my players convinced that Astalle was the the key until they finally realized she was a bored goth chic. Ayn was the most fun because I played her as a crazy, irrational religious zealot. When the party started digging into her world view she finally was tripped up over her own logic and spilled the beans in a pendantic, "here is what is wrong with the world" monologue (this was done in the context of a skill challange, though I don't say "we are now in a skill challenge."*)
The Woodcutter's Cottage is good for the creep factor.
For time's sake consider skipping the Carriage Graveyard.
For Infested Tower, Ham is one of my all-time favorite monsters. Ham it up, pun intended, and play the gross factor to the hilt.
Only include one of "Parts is Parts" or "Carnel Pit" for time's sake. With Charnel Pit I added some monsters and broke it into two parts (though with no short rest). I used the hag's shape change to get the party to go through an elaborate and messy search process in the liquified flesh to rescue the "maiden" before the second wave came. Fighting while submerged in flesh goo is a good opportunity for descriptive text, circumstance penalties and acrobatic stunts.
The final fight is tricky. I had Festaud sneak in and "charming kiss" a character ("My hero! My hero! <smooch, smooch, smooch>. Then I said to the player/group, "Here are the mechanical effects. I will will leave it up to you if you want to go with it and roleplay as if you are ensorcelled or if you want to just play the mechanics." The player choose the fun path and the rest of the group played as if the did not know that he was charmed. This actually made the fight kind of easy since Festaud was not a combatant. If I were to do it again I would have monsters from "Parts is Parts" come in over the course of the fight until I determined the party was appropriately challenged.
If you want to leave the opportunity open for further adventures, in my game while traveling back I had Festuad convice the charmed character to let him step out, stretch his legs and have some private bathroom time. By the time they got home Festaud escaped and all the witnesses were dead. Of course, this depends on your players playing along.
*I try to keep skill challenges organic so in this case I would have two or more skill challenges running simultaneously. The physical searching would be one and the questioning of important NPCs would be one more each. For insignificant NPC I would still let the players roll but the results would be mostly immaterial (aside from, say, "you rolled a 5 for insight? For all you know 'she' is a 'he' and 'he' is your daddy in disguise.)
and it was a fun adventure.
