Talk to Elena in a house just west of the East Ardougne north bank, across the river.
Talk to Jerico, who is in the building south of the Ardougne north bank.
Search the cupboard near Jerico for some bird feed.
Go behind Jerico's house and pick up a pigeon cage.
Go back across the river, west of the castle to the West Ardougne gate.
Use bird feed on the watchtower fence (the spears, highlighted in red on your minimap) where several Mourners are perched above, and open the pigeon cage.
Talk to Omart, south of the gate to West Ardougne, along the wall at the corner.
Talk to Omart again.
Martha Rehnison's House
Go to Martha Rehnison's house, highlighted in the picture, north-west of where you breached the wall.
Take the rotten apple on the east side of the house.
Squeeze through a gap directly east of the rotten apple, along the west side of the metal fence.
Use the rotten apple on the cauldron in front of you.
Go back through the fence and attempt to go into the house, a mourner will stop you.
Go to Nurse Sarah's house in the corner, south-west of the church.
Search the box on the north side of the house to obtain a doctors' gown.
Equip the gown.
Go to the north-east corner of the city, and enter the Mourner Headquarters.
Open the door to the west and go upstairs
Open the door to the east and kill a Mourner to obtain a key.
Use the key on the gate in front of you to get into the caged room.
Search the north-eastern Crates to find the distillator.
Return to the West Ardougne city centre, and exit through the manhole.
Talk to Elena.
Without teleporting, go to bank and deposit your plague sample. Teleporting with the Plague Sample in your inventory will destroy it, forcing you to retrieve another sample from Elena.
Retrieve the plague sample from the closest bank to Rimmington and walk there. ( Skills Necklace teleport to the Crafting Guild is the quickest.)
Enter the western most house in Rimmington and talk to the Chemist. (Do not mention that you have the sample or he will take it away from you and you will be forced to go back to Elena to get a new one)
Talk to Chancy.
Talk to Da Vinci.
Talk to Hops.
Deposit your plague sample back in the bank and go to Varrock.
Delivering the Samples
, Plague Sample, Priest gown top, Priest gown bottoms
Obtain the plague sample from the bank.
Go through the gate south-east corner of Varrock.
Talk to the 3 chemist's assistants at the Dancing Donkey Inn to get the vials back.
Equip the priest gown top and bottoms now.
Go to the building south-east of the pub and go inside.
Talk to Guidor, tell him you are sent by Elena, and give him the samples.
Talk to Elena.
Go to Ardougne Castle, south of Elena's house, and climb either the stairs to the north or south.
Talk to King Lathas, who is in the middle chamber of the 1 of the Castle.
st floor [ UK] Quest complete!