BIOHAZARD QUEST WALKTHROUGH
Elena: She will tell you to talk to Jerico, find him in a house south of the west bank. He will tell you to talk to Omart found at the southern wall.
Omart: After talking with Elena head over to Omart who will tell you that you'll have to talk with Jerico about something to distract the guards. Jerico will just send you back to Omart because he's too busy feeding his pigeons. While at Jerico, search his cupboard to find some pigeon feed, and go around back and take a pigeon cage.
Over the wall: Go to the tower north of Omart and use the pigeon feed on it, and then release the pigeons. Talk with Omart and get over the wall. Now go all the way north and take a rotten apple west of the most north-eastern house there. Now go over the fence, use the rotten apple with the cooking pot, and talk with the mourner.
Doctor: The mourner will tell you that they're all sick, so you'll have to play a doctor now. To do this you'll need a doctors gown, you can find this in the house south-west in the city where the nurse Sarah lives. Search the cupboard to get the gown. Put it on and go back to the mourner. Open the door to the building and go upstairs, where you'll find a mourner you'll have to kill.
Elena's distillator: After you kill the mourner upstairs you'll get a key. Use this on the gate over there, and search the crates in there. Go back to the place you came over the wall and get Kilron to help you over. Head back to Elena, and she'll tell you to take some samples to the chemist in Rimmington. Be careful with the samples, they will break if you teleport or fight on the way. You can put them in the bank and teleport to Falador though.
Chemist: Once at the chemist’s house a little west of Rimmington, talk with him (don’t talk about the plague), and then go outside and give Chancy the liquid honey, Hops the sulphuric broline and Devinci the ethenea (in that order)
Varrock: Go to Varrock and buy a priests robe from the clothes shop if you haven’t done that already. Go to the Dancing Donkey Inn in south-east Varrock and get your samples back from the three men there. Put on your priest robes and head into the building where Guidor is. Talk with him, and he'll tell you that there is no plague. Go back and give Elena the good news, and then head over to the King for your reward.