Forge of Fury as a mystery/puzzle (help wanted) [spoilers]

[freyar]

Ok, so I'm all set to start Forge of Fury up soon (with 4th level characters and a 5th level NPC tagging along part-time). For campaign and speed reasons, I'm making the following changes:

1) Replacing the orcs with hobgoblins.
2) Basically getting rid of the troglodytes on the second dungeon level.
3) Getting rid of the undead on the 3rd (duergar) level.
4) Inserting a mid-level NPC wizard who has been feebleminded by a lucky duergar wizard (with a scroll). The duergar are willing to trade the captive in exchange for the PCs getting rid of the dragon, letting the PCs rescue someone they've been curious about for a while.

So, after I've planned all this out, I'm realizing that my wife (one-on-one campaign, 2 PCs for each of us, and I'm relatively inexperienced DMing) prefers by far mystery or puzzle type challenges in each session. It doesn't need to be anything major, but something to avoid lots of major combats. (That's part of why I'm getting rid of the trogs.) But I need some ideas; anyone want to help? Thanks!

And, if you want to, I be happy to hear suggestions of an appropriate reward for a 10th level diviner to give a party like this once she's back to herself...

Thanks!

 

[Peni Griffin]

The big mystery for my party was what the hail the original dwarfs were thinking putting all those traps on high-traffic areas...

The duergar are there on a secret mission, so finding them is puzzle one and deciphering their lies about why they're there is puzzle two. Without the trogs level 2 is going to be pretty empty, leaving you plenty of room for clues.

 

[Klaus]

When I ran it, I not only kept the trogs, I actually expanded their lair into a chapel to the Tentacled God (the roper). I turned the leader into a cleric (wanted it to ba an iconic trog, so I went for their favored class), and put clues in the chapel (paintings on the wall) showing the trog holding the Tentacled God's wrath at bay with torches while making a sacrifice. This lets the PCs deduct that the thing was immune to fire.

 

[freyar]

Klaus, that's a pretty cool idea, which I'll probably yoink if I run this in a different campaign. I wanted to keep the hobgoblins as a foreshadowing/hint of a forthcoming goblin war, so I needed to lose either the troglodytes or duergar to keep this from becoming too much of a crawl. The duergar seem to have more potential for capturing a wizard, so...