QUOTE(jack cloudy @ Feb 22 2008, 07:12 PM)

Ok, I've never had this problem. Cause I'm a goody two-shoes holy saint.....except when dealing with Telvanni and outlaws.
Anyway, what are you playing? PC, or X-box?
If on the PC, I suppose you could open up the console and type in the codes you need to get the item and further the quest. I think the first one was something along the lines of: Pcadditem xxxx (With xxxx being the item id.)
Anyway, check the constructionset for the id of the notes and the journal. Oh, and you'd better get the help of someone who knows a bit more about the console.
If on X-box, I can't give you any surefire solutions.
1: Does Caius consider the quest unfinished? If he doesn't have a problem with two out of three, you're fine.
2: Try to get rid of the guy anyway. This probably involves killing him at this stage. Although, I honestly doubt Bethesda placed a flag in the quest to deal with killing the agent after you revealed the kitten's hideout.
3: Try pickpocketing Adhirranir. Maybe she has the notes.
4: If you can't pickpocket and absolutely don't know a way out, kill her and see if you can get the notes that way. This one is definitely a desperation act, so save beforehand.
5: If absolutely nothing works, you'll be limited to either returning to an earlier save. (though if you're anything like me, you already saved over your older saves before noticing the problem.) Either that, or take the back door to the Main quest. (which I've never done but sounds really lame compared to the real main quest.)
Edit: Are the notes really needed? I don't remember ever losing my notes to Caius.
Thank you. I play on PC game of the year edition so I'll try looking att the construction set.