This walkthrough was put together by Skullcracker while the old DSotSC message boards were still up. If, after you read this walkthrough, you still have questions go to the DSotSC message board at the DSotSC site.
By popular demand, here you go, the quests in order;
Everything begins with you flooding the Cloakwood Mines. This starts Chapter 5. As soon as the mines are flooded, prepare your party to take on a new NPC. She's an elven cleric. (i.e. strip the NPC to be dumped of all magic items, and dump him/her in an area that you can pick him/her up later, if you choose - inside buildings are recommended). It is also recommended that you sleep as soon as possible, so the Chapter 5 dream sequence runs.
The quests must be completed in this order, save the Dark One, which can be done anytime, except as the last quest. The missing nephew quest reset all of my new Dark Side areas (i.e. removed them) when I completed it. I don't know if this was specific to my game, or was supposed to happen. So play safe, and assume it will happen to you.
Go to the Friendly Arm Inn map. Jet will seek you out if you head to the southern portion of the map. Take up her quest to find her sister and have her join your party. As soon as you do, the Forest of the Forgotten Souls maps should highlight on your world map, and the Dark Side intro program will run. This is similar to your dream programs in between chapters, except the narrator sounds like Sean Connery speaking into a paper bag (Sorry CúChoinneach, couldn't resist).
To access the LS maps you need to go through Peldvale. People have trouble finding the access, so the co-ordinates are x=5020, y=638, map 2400. Co-ordinate access is achieved by pressing the "L" key on your keyboard, and it pinpoints the location of your mouse pointer. There are 3 LS maps. The first is inconsequential. On the second map, you must observe the phantoms doing battle for a while. Just stand and watch. Nothing happens, but it is a prerequisite for what will come. Be very careful on these maps, as undead exist that can and will suck your experience and levels. Quick save after each little battle, AFTER you have checked that you haven't been sucked for XP. If you have, resume from the previous quick save. This will save you a world of grief
Enter the last LS map at night. As close to midnight is best. It has been reported (but I have yet to confirm this) that you also need to clear out the undead nasties that are located in a cavern in the north central portion of this map. Play safe and clean it out. Now you have to search for Jet's sister. She reportedly moves around this map, but I have generally found that she is pretty close to the cavern that you cleaned out. You know you are close when you hear wailing and moaning.
When you find her, Jet will engage in conversation and ask if you still want to help. You better say "yes" else you are screwed. On her sister's body is a necklace of importance. Right click on it for a very helpful game hint.
After you polish off the sister, the Dark One quest is normally next up. The Dark One quest does not find you (as all of the other quests do). When you finish Jet's quest, walk back to the map where the phantoms and cabin are located. Sometimes the phantom will talk to you, and sometimes you have to talk to the phantom. The Dark One is located very close by, so it takes very little time to complete; however the battle is of epic proportion. You will find that you have to kill the Dark One (be careful as he teleports away, and this does not count as a kill), and then the phantom will ask what's taking so long. He then informs you that you need the Dark One's life essence that is located within the cabin (this is the trigger for the cabin access). Get the stuff from the cabin (which the Dark One may be guarding from the outside), kill the Dark One again, and pick up the 6 potions that are on his body. Take the 6 potions to the phantom and everyone is happy (except the Dark One, as he's dead). Be careful not to kill the phantom in all of the battling. He is vulnerable to attacks after the first time he talks to you. He is also affected by turning undead, so be careful if you use this power.
Upon finishing this battle (and finding some very cool treasure), make sure you return Jet's sister's necklace (the tear necklace) to her family member located in the Jovial Juggler Inn (Beregost). He will give you a letter that allows you to have a special mace made. Take the letter to the Thunder Hammer smithy weapon shop. Otho will commence the construction of the mace, which will take 5 days.
A child should approach you to go to the Red Sheaf Inn (or was that the Burning Wizard, I forget). You will meet the priest of Morningwhatever. He says that he has recently lost a religious relic, and you are to return it to him. Accept the quest, then go to the Nashkell Inn. You will meet Jeremy (mayor's assistant), who asks if you will vanquish the dragon. Also at the Nashkell Inn is Strongblade. He asks to join your party to help slay the dragon. You might have to wait a few minutes in the Inn, as Strongblade enters from the rear room area AFTER you have decided to take on the dragon quest. Now you're off to the races.
On the way to the dragon map (just south and east of Nashkell), you will meet a halfling thief. He is a decent thief, and you can ditch Imoen if you want. He also carries 6 or 7 arrows of green dragon slaying.
Upon approaching the dragon (east central area of the map), you will encounter numerous gnolls that do nothing but piss you off as you get ready to do serious battle. Try and kill them off without initiating the dialogue with the dragon.
As for battle tactics against the overgrown lizard, I will leave that up to you.
After you kill the dragon, you need to find his hoard. The access is located a little to the west, on a mountain facing (still within view of where the dragon was sitting). You need to find the hoard, as that is where the religious relic is located, along with more cool treasure. If anyone in your party is proficient with battle axe, you will love the weapon in the hoard.
Now you return to Nashkell to return the religious relic to the cleric , as well to get your rep. points from Jeremy (the mayor's assistant). On the way a little girl will approach you. You have to be nice to her *evil character grimaces* and then the game goes on autopilot as everyone gets taken to the mayor's house. You now regain control of your game, enter the mayor's house, and talk to the mayor's wife about her missing child. Ask who had access to the child.
You resume heading back to return the relic and get your rep. points. Outside of the Nashkell Inn is a lady that tells you about a lost necklace just to the north. Help her out. On the way you meet CúChoinneach and his damn dog. He fills you in on the child/vampire issues, and the Citadel should now appear on your map.
In the interim is the special mace. You should have had this put into production (as it is made by Otho at the weapon smith's shop). You go to pick it up, and when you exit the shop, Elminster talks to you and empowers the mace. He then says you should have it blessed by a cleric.
You remember that after you returned the religious relic to the priest of Morningwhatever, he said if you ever need anything, you can find him at the temple, located just east of the Friendly Arm Inn. You go there, have him bless the mace, and now you can find the access to the Citadel (the access will not appear until the mace is blessed). You find the access on the east (or was it north) boundary of the map that you fought the dragon.
If you thought there were a lot of undead on Jet's quest, you haven't seen anything yet! It is highly recommended that you keep Jet for this quest (but not essential). Jet and CúChoinneach make a dynamite front line against the undead.
After numerous levels of the Citadel (don't forget the upper levels, as there is a +3 vorpal weapon hidden in the top level chimney stack) you will encounter the baby sister. Demand the return of the baby, and prepare yourself for battle. There is some dialogue with CúChoinneach and the vampire, and after a few spells, the head vampire buggers off.
After more undead battling, you should find him (and the babysitter) waiting for you not too far away (end of a long corridor). This is where things can get dicey. If you are lucky and kill him on this screen, you get transported to his tomb/crypt where you find the baby. If he gets away, you have a bit of search ahead of you.
You will find the map that is the template for the basement of the Candlekeep map. There are several corridors that are seriously trapped, but contain great treasure. There is one corridor that appears to be a dead end - BUT it is not. You will find stairs going down. Take them after you have cleared the remaining areas.
This lower level is maze like and contains more, you guessed it, undead. You have to meander around to the north, west, south and then back east to get where you want to go. The head nasty (and maybe the babysitter) are located in the small area furthest to the east. After you finally kill them, there is an access on the east side of this small area that leads to the crypt. Again, nice treasure - but don't forget to bring the baby back. If you have killed any of these nasties previously, it is possible to get numerous babies, but don't worry, it doesn't affect the quest. Bring the baby back to his mother and get the rep. points.
The next (and last) quest begins with you being summoned to the Hammer smithy shop again. Otho (who made your mace) is looking for his nephew. He went missing somewhere between Beregost and Nashkell. Obviously, take up the quest.
You are looking for a campfire that is located on one of the maps indicated. It is just to the left of the main road. There is an access somewhat concealed (not hidden) on the mountain rock face just to the left of the campfire.
What will follow is a whole host of maps until you find a map that looks like the main floor of the Flaming Fist headquarters (in BG). SAVE THE GAME IMMEDIATELY. As you enter the room you will find Trollslayer doing battle with about 50 Duragar (underground dwarves). He will ask if you want to help him. Duh, say yes. When the fight is over talk to Trollslayer (awesome Dwarven fighter) and have him join your group. He will tell you that "the bastards killed the nephew," but will want to investigate the unnatural recent goings-on. There have been major problems with getting Trollslayer to join your party, so if he doesn't respond to you, you need to download the Trollslayer fix file from the Dark Side home page and unzip it in your override file (I think that's where it goes, just follow the instructions). Resume playing from the game that you strategically saved just before the battle.
You will go through seemingly endless mazes, and will either encounter the Drow leader or a very very nasty undead beast. Either way, these battles are great, and I'll let you figure out how to deal with them on your own. It is stressed that on all of the maps that you venture through, that you look for ALL accesses. There are a few that wouldn't expect to find. Search for them all, as there is a pile of treasure just waiting to be had.
You now have to venture back (very long walk unless you found the Bandit Camp access) and tell Otho about his nephew. He takes the war hammer that Trollslayer has and guess what? You have now finished the Dark Side quests. As a word of advise, read all of the books that you find in the Drow leaders quarters, one of them has some interesting facts about the game.