Bloodmoon:The Moon Sugar Mystery

Quick Walkthrough
# Talk to Severia Gratius in Fort Frostmoth's courtyard.
# Talk to Jeleen in the Imperial Cult Shrine.
# Travel to Uncle Sweetshare's Workshop south of Lake Fjalding.
# Obtain his White Colovian Fur Helm, whichever way you choose.
# Return the helm to Severia Gratius.

Detailed Walkthrough
Moon Sugar Investigation
Severia Gratius in Fort Frostmoth's courtyard needs help with a moon sugar investigation. It seems that during the past few months, several people across the Island have been poisoned with the contraband for reasons unknown. Keep inquiring further and agree to help her find, and kill, the culprit. The most recent victim, Jeleen in the Imperial Cult Shrine, saw the suspect and describes him as a man wearing a unique white Colovian fur helm. You must bring this helmet back to Severia Gratius as proof that you've killed him. 

Detective Work
Talk with Jeleen in the fort's  Imperial Cult Shrine about moon sugar investigation. He will mention the strange hat worn by the strange old man who probably wasn't a Nord. The man also sang a very silly song, like a nursery rhyme mentioning something about a workshop, snow, candy, and ha ha ho's.

The problem now is where to look. Jeleen does not have any more to add, and Severia refuses to speak to you until you find and kill the person involved. No one else around the Fort has anything to say about the matter, either. The best bet is to go out and see if you can find this workshop in the snow, or simply wait until you happen to come across it during your future travels around the island.

The Workshop
The workshop in question, Uncle Sweetshare's Workshop ( ), is northeast from Fort Frostmoth and south of Lake Fjalding. Outside is the body of a dead Khajiit, M'nashi, with some moon sugar and a copy of the song Jeleen mentioned (which increases your Alchemy skill). You will find Uncle Sweetshare inside, and he will gladly tell you of his exploits in "spreading the happiness". He also admits to being involved in the death of his assistant, M'nashi, who apparently had too much moon sugar. Keep inquiring and you will soon give the Uncle the choice of death or promising to stop (and giving you the white helm that you need). 

Choosing to murder Uncle Sweetshare will also let you complete the quest successfully. Upon returning to Fort Frostmoth, talk to Severia Gratius, who will take the helm and reward you 1500 gold.  If you are a member of the Imperial Legion, Severia Gratius will also give you her enchanted shortsword.

Notes
If Uncle Sweetshare reminds you of Santa Claus (Father Christmas), you're not far off.  In fact, it seems that prior to release, the character was named "Grandfather Frost" (similar to "Father Christmas"), and wore a Red Colovian Fur Helm, rather than white - even more Santa-like.  He even had a different song: The Song of Grandfather Frost.  Evidently, they decided that this was just a little too close to Santa, and changed a few details.
You will have to have completed the "Rebellion at Frostmoth" quest before Severia Gratius will appear in Fort Frostmoth's courtyard.
If you refuse the quest, and are not a member of the Imperial Legion, Severia Gratius' disposition will drop by 10 points and you also lose five points with the Imperial Legion faction reputation. If you are in the Legion, her disposition drops by 15 and you lose ten points of reputation.
Half your faction and disposition reward comes when you accept the quest, and half upon completion.

Bugs
 
As long as The Missing Missionary quest is complete, this is of no actual consequence, since he has little to add to the current quest, and no additional ones to offer. You can bring him back if you want, with a Console command such as  .

Quest Stages