Biohazard

To begin speak to Elena in East Ardougne (directly west of shortcut log). Dialogue: I'll try to retrieve it for you.

Speak to Jerico in the house just south of the northern Ardougne bank (The house with pigeon cages in the backyard).

Search the cupboard to obtain bird feed (click continue or the bird feed won't be added to your inventory).

Grab a pigeon cage from the backyard (note: if you are planning on doing One Small Favour, grab an extra 5 pigeon cages).

Go south-west of Ardougne Castle and speak to Omart.

Go north to the small watchtower along the wall, in front of the gates to West Ardougne.

Stand in the corner where the two spiked fences meet.

Use bird feed on the watchtower fence.

Click open on the pigeon cage in your inventory.

Equip your gas mask.

Run south from the watchtower and speak to Omart. Dialogue: Ok, lets do it. After a slight delay, you will arrive in West Ardougne.

Head around the headquarters to the north-eastern area with the vat and mangle.

Squeeze through the fence into the backyard.

Pick up the rotten apple.

Use the rotten apple on the cauldron.

Go back through the fence.

Go to Nurse Sarah's house, south-west of the West Ardougne church.

Search cupboard in northern part of the house for a medical gown.

Equip the medical gown, go back to the headquarters and open the door.

Go upstairs and kill a mourner. A key will automatically be placed in your inventory.

Use the key on the gate to get into the caged room.

Search the crate third from the left on the northern wall to find Elena's distillator.

With 3 empty inventory spaces, return to Elena and give her the distillator (via Ardougne Teleport, Skills necklace teleport to the Fishing Guild, over the wall by Kilron, or via the sewers from the Plague City quest).

Go to the Chemist in south-western Rimmington (you can take a ship from Captain Barnaby at the Ardougne Dock directly to Rimmington for 30gp or use a teleport as the vials won't break upon teleportation anymore)

Speak to the Chemist. Dialogue: Your quest. He will give you the touch paper.

You will find Chancy, Da Vinci and Hops around a fire outside the Chemist's house.

Give Chancy the Liquid honey. Dialogue: You give him the vial of liquid honey...

Give Da Vinci the Ethenea. Dialogue: You give him the vial of ethenea...

Give Hops the Sulphuric broline. Dialogue: You give him the vial of sulphuric broline...

If you happen to give the wrong item to one of the henchmen you must then give the rest of them an item and talk to each one of them in Varrock before being able to give them the correct items again.

Teleport or travel to Varrock.

Travel to the fenced area to the south-east of the bank (south-eastern Varrock). The guard will search you, but you will be able to pass freely with the plague sample and touch paper in your inventory.

(Optional) Speak to Asyff, the Fancy dress shop owner, in the building south-east, to get a free priest gown (top and bottom) and equip it. Alternatively, purchase a priest gown (top and bottom) from him and equip it.

Go to the Dancing Donkey Inn.

Talk to Hops, Da Vinci and Chancy to get the vials back. Make sure you have the free inventory space.

Do not pass back through the gate or your vials will be confiscated by the guard and you will have to get new samples from Elena again and continue the quest from that point.

If you must pass through the gate to retrieve the plague sample or papers, you can drop the vials at the gate, quickly run to Varrock east bank for the items, and run back to pick up the vials.

With your Priest gown equipped head to Guidor's house in the south-east of the fenced area.

Speak to Guidor, tell him Elena has sent a sample that needs to be processed. Dialogue: I've come to ask your assistance in stopping a plague.

Return to Ardougne and speak to Elena.

Go to the first floor of Ardougne Castle and speak to King Lathas. Dialogue: I don't understand...

Congratulations, quest complete!