Plague City

Gathering the items
Most of these could be bought at the Grand Exchange.
 * Dwellberries spawn in McGrubor's Wood west of Seers' Village. You can get in by squeezing through a loose railing on the north side. You may also buy dwellberries in the Tree Gnome Stronghold or even grow them yourself using Farming.
 * Rope can easily be bought in the general store in Ardougne.
 * Milk can be obtained by using a bucket on a dairy cow. There is a pasture of cows directly south of the Ranging Guild. It also may be bought in the Tree Gnome Stronghold.
 * Chocolate Dust can be obtained by using a Pestle and mortar or a knife on a chocolate bar, which you can buy at the Baker's Stall in East Ardougne for 20 coins. Chocolate bars can also be bought in Yanille, Nardah, or Port Sarim, or can be found in the Cook's Guild. It can also be bought in the Tree Gnome Stronghold. If you have started Recipe for Disaster, it can be bought at the Culinaromancer's Chest.
 * Snape grass is most easily obtained on the small peninsula that is to the west of the Crafting Guild or by purchasing it from the grand exchange.
 * Elena's picture can be found in Edmond's house. It's on a table.
 * Buckets can also be obtained from Richard at the farm north of Ardougne.

Starting the quest
Once you talk to Edmond, he'll tell you to talk to his wife about getting some sort of protection against the plague. His wife is just inside the house, and she'll tell you she can make a gas mask if you get her some dwellberries. Give her the berries, and she'll give you a mask. If you lose the mask, there will be one in the wardrobe. Also, make sure you get a picture of Elena while you're there.

Talk to Edmond again, and he'll tell you about his plan to dig under the wall and get into West Ardougne. First you'll need to soften the ground, though. Use your buckets of water on the mud patch in his garden to make the soil soft enough to dig into, then use a spade, which you can find nearby, to dig through into the sewers. You'll find Edmond inside as well. Walk to the south, and you'll find a pipe blocked by a grill. Try to open the grill, and you'll find that you're not strong enough to pull it off alone. Talk to Edmond, and he'll suggest you tie a rope on it so you can both pull it off together. Just use a rope on the pipe and talk to him again to pull the grill off. Put on your gas mask and climb inside to go into West Ardougne.

Note: If you need to go back for anything, there is a mud pile you can climb up to the east of the long sewer corridor, you don't need to panic and teleport out.

Finding Elena
Once inside West Ardougne, talk to Jethick. He's standing nearby. Show him Elena's picture. He'll tell you to go check the Rehnison house and give you a book that he borrowed from them. The house is located north of the town square. They'll let you in when you mention you have the book. Once inside, talk to Martha Rehnison and then go upstairs and talk to Milli the daughter of the household who'll tell you more about Elena's whereabouts.

Head back out of the house and south of the town square to find the house the girl told you about. You'll recognise it because of a big black "X" on the door. The house you seek has two doors, both facing North. It is behind a row of crumbling houses just south of the town square. Unfortunately, the Mourners won't let you in because it's been hit hard by the plague. Tell them that you're looking for a kidnapped girl and that you want to check even though Elena is probably dead. They'll tell you you need to apply for clearance from Bravek or the Head Mourner, however you can't enter the headquarters to get to the Head Mourner. You'll need to speak to Bravek to gain the warrant. Speak to the clerk on the first floor of the house by the manhole which you first came in through.

Getting inside and finishing the quest


Go back to the town square and go into the large building just north of the manhole. Tell the Clerk you're there for something very important and he'll let you inside to see Bravek. He is located upstairs in the eastern most room. He can hardly talk to you, though, as he's badly hung over. He'll give you a scruffy note with a recipe for a hangover cure. You must get the scruffy note from him to complete the quest, even if you already know how to make a hangover cure. To make it, put the chocolate dust into the bucket of milk (be careful not to drink the chocolate milk) and add Snape Grass. Give the concoction to him, and he'll give you a warrant that grants the permission you need to go search for Elena in the Plague House.

Head back to the house and try to enter again. Use the Warrant on one of Mourners to show it to him. They will talk amongst each other about the legality of the warrant, giving you a chance to sneak inside. Search the barrel on the west side of the staircase to find a small key. Then go downstairs to the basement and unlock the cell door to release Elena.

Head back to the manhole in the town square to get in the sewers, and talk to Edmond to end the quest.

Rewards



 * 1 Quest Point
 * 2425 Mining experience
 * A magic scroll, letting you use the Ardougne Teleport if your Magic is 51 or above. And also to use Ardougne teleport tab. After you read it, you'll memorise the spell.
 * Ability to make an Ardougne Teletab
 * Gas mask
 * Access to West Ardougne
 * Ability to have a Ardougne teleport in your house.

Music
Music tracks unlocked:
 * The Cellar Dwellers
 * Sad Meadow

Trivia

 * If you "Unlock Hint" the song Cellar Dwellers it will say "This track was unlocked during the Hazeel Cult."
 * If you use the drop trick to obtain two magic scrolls and try to read the second one, "The scroll bursts into flame." and deals you some damage.