The Uncommon Cold

The Uncommon Cold is a quest that can be undertaken in Chapter 10 of Baldur's Gate: Siege of Dragonspear. It is triggered by talking to Dosia in the Coalition Camp.

Background
A strange plague has befallen several of the warriors in the Coalition Camp, resulting in a triage area being set up in the southwest of the camp. Dosia, the lead healer, is completely baffled by the disease and has no idea how to cure it, instead being kept busy trying to keep the people alive. Speaking to Dosia gives the player the quest to examine some of the sick and try to identify a possible solution.

Examinations
The player must speak to three sick soldiers; Xerra, Yestimell and Zidrand. The order in which they are investigated doesn't matter. You will need either Glint, Jaheira, M'Khiin or [Viconia in your party to analyze the symptoms.

Xerra will be noted as feverish, and your chosen healer will recommend the use of a cooling poultice.

Yestimell will attack the party in a pain-fueled berserker rage, and must be slain. If your party includes Corwin, Jaheira or Minsc, they will compare Yestimell's behavior to that of a plague-maddened forest-rat. This unlocks the "Ask a Rat" option.

Zidrand seems sicker than the others around her, and your healer will deduce that close proximity between the infected intensifies the effects of the disease.

Unconfirmed

 * Gorion's Ward may be able to analyze the symptoms and deduce a possible means of curing the disease if either their Wisdom is sufficiently high or if they have the Cleric, Druid, Ranger or Shaman class.

Reporting
Once all three sick soldiers have been investigated, the player must speak to Dosia about their findings.

If the player's party includes Glint, Jaheira, M'Khiin or [Viconia, they can be asked for advice, and they will recommend the player use a poultice of Blackthorn Tree bark.

If the player's party includes Corwin, Jaheira or Minsc, the player can mention their comment to Dosia, and she will suggest that they ask a rat for advice.

The player can also suggest either simply quarantining the infected and letting them ride out the disease (fails the quest) or that they be executed (fails the quest, -2 Reputation, counts as a Villain point for the chapter 13 ending).

If the player asks Dosia for her opinions on what to do, she will recommend going to the nearby Bloodbark Grove and speaking to a local druid named Onoroth for advice.

Ask a Rat
The player must use either Corwin, Jaheira or Minsc to speak to rats running around the camp. The first rat will turn into a hostile wererat and attack the party. The second will reveal the cure to the disease is made from Blackthorn Tree bark, essentially making this a slightly longer and more EXP-generous route to the answer that Glint, Jaheira, M'Khiin or [Viconia could have given you in the first place. See "Get Blackthorn Bark".

Ask Onoroth
Onoroth can be found near the ruined house in the south-east corner of the Bloodbark Grove map. He will reveal that he can make a cure, but he has a request first; the player needs to kill a Diseased Greater Basilisk in the northwest corner of the map and bring him its claw as proof of the deed. Once this is done, he will give the party a dose of Blackthorn Bark Cure.

It bears mention that it's possible to kill the basilisk and take its Basilisk Claw even after this quest has been completed without Onoroth.

Get Blackthorn Bark
The Blackthorn Tree is located in the northeastern corner of the map, near a Shambling Mound and a pack of Bombardier Beetles that are guarding a corpse that carries a Clasp of Helm, a scroll of Conjure Lesser Earth Elemental, and a Wand of Fear. The tree is noted on the map as a "Strange Tree".

When the tree is interacted with, a pack of mixed wolves and dire wolves will attack the party. The dire wolves will display trollish regeneration for some reason, and must have fire or acid applied to their downed bodies to kill them. Once the bark is collected, it is automatically transformed into Blackthorn Bark Cure in the party's inventory.

The Cure
When you return to Dosia, you'll have three options:
 * If you just hand over the cure, then you'll receive the Martyr's Morningstar +2, +1 Reputation, and 6000 gp, as well as gaining a point towards the "Heroic" ending in chapter 13.
 * If you demand payment for the cure, then you'll receive three Potions of Extra Healing, -1 Reputation, and 6000 xp.
 * If you tell Dosia that her payment isn't good enough, then you'll receive -2 Reputation.

Once the plague is cured, Dosia may be used as a standard temple healer.