This guide is suitable for current RuneScape and Old School.
Talk to Elena in her house on the opposite side of the river from the bank. She will tell you the Mourners have taken her Disstilator and she needs it to find a cure for the plague. Offer to help her and she'll send you to Jerico who lives south of the bank.
Jerico will send you to talk to Omart who is at the south of the West Ardougne wall, near the spirit tree. He'll tell you that you need to find a way to distract the mourners in the watchtower, he'll send you back to Jerico. While at Jerico's house he'll tell you he is busy and sends you back to Omart. While here search the cupboard and you will find some bird feed. Go round the back of his house and pick up a pigeon cage.
Head over to the watchtower and use the bird feed on it. The choose the option to open the pigeon cage, you will get a message telling you they are being distracted by the pigeons. Now you have to go see Omart again. He'll send you over the wall.
Head to the Mourners HQ and try to get in, you won't be allowed in and you need to find a way to distract them. Head back over the wall and head to the Apple Orcid Near the Gnome Stronghold. Pick up some rotten apples and head back to the mourners HQ, but this time go round the back until you find a fence that you can go through. Use the rotten apple on the Cauldron.
Head Back round to the front door and try to get in. You won't be allowed in and you will get the message that the Mourners have got food poisoning and that they need a doctor. Head to Nurse Sarah's house on the east side of the graveyard in the south west of the city. Search the cupboard and you will find a doctors gown. Head back to the mourners HQ and head straight to the top floor. Talk to the mourner there, he will attack you, kill him and he drops a key.Open the gates and search the crates to find the Distillator.
Going to Guidor
Take it back to Elena and she will tell you that the test she does shows nothing. So she sends you to her old mentor Guidor who lives in Varrock. She will them give you a Plague sample, liquid honey, sulphuric broline and ethanea. But first you need to go to the rimmington chemist and get some touch paper. TELEPORTING OR ENTERING COMBAT WITH THE SAMPLE WILL CAUSE THEM TO BREAK AND YOU WILL HAVE TO GO BACK AND GET SOME MORE.
Head down to the port and take the ship to Brimhaven, charter the ship to Port Sarim and run to the chemist. When you get there DO NOT TALK ABOUT THE PLAGUE HE WILL TAKE THE SAMPLES FROM YOU AND YOU WILL HAVE TO GO TALK TO ELENA AGAIN. He will tell you that the Guards in Varrock are looking out for plague carriers, and you will have to use his couriers outside.
Give the Liquid Honey to the gambler Chancy. It's valueless so he won't be able to sell it. Give the Sulphuric Broline to Hops, he's a alcoholic so he won't be able to drink it since it's poisonous. Give the Ethanea to Da Vinci, he's a painter so he can't use the colourless Ethanea to paint with.
Head to Varrock with the touchpaper and the plague sample. DO NOT TELEPORT THE SAMPLE WILL BREAK. When at Varrock, head to the Dancing Donkey Inn which is near the fancy dress shop. You will get searched but he will let you through. Talk to the 3 people and get the sample back. This is when you use your priest robes, Guidor lives south of the Fancy Dress shop, but his wife won't let anyone see him, and she wants him to talk to a priest. Where the priest robes and go through the door. Give him the samples and he will tell you that there is no plague, and someone was making it up.
Head back to Ardougne and talk to Elena, who will send you to the king. He will tell you the truth about why the plague was faked. You will now receive your reward.
Congratulations! Quest Complete!
Guide Made by: Rural Life
Corrections submitted by: Doctor Shemp, Jamie, Runis Altair, Power of Five, Tiny, Philby25