Start: Talk to Hetty in her house in Rimmington, south of Falador and west of Port Sarim.
Items needed: Burntmeat, an eye of newt, an onion and a rat's tail.
Monsters to kill: Rat (Level 2)
Talk to Hetty in Rimmington and tell her to help you become one with your darker side. She will then ask you to get her 1 burntmeat, eye of newt, an onion, and a rat's tail. In exchange she says she will increase your knowledge of the dark arts (Magic).
Tail of rat
Kill a level 2 rat. They can be found all over Rimmington, so you should have no trouble finding one. if you find yourself not getting a Rat's tail drop then that means you have not yet started the quest.
Walk north a little way and you will find a patch of earth with onions on it. Take one.
Eye of newt
Head east to Port Sarim, enter the Magic Shop and speak to Betty. Buy an eye of newt for 3 coins from her store. If there is no remaining stock, wait for the stock to replenish.
If you don't already have raw meat, kill the giant rat south of the Port Sarim jail and cook the meat it drops (there's a range in the building west of Hetty's house). If you don't burn it, and get cookedmeat instead, use the cookedmeat on a fire or range, and you'll get burntmeat. You can also get burntmeat by killing Imps.
Head back to Hetty and give her the four items by talking to her. Right click the cauldron and select drink-from.
1 Quest Point
Between 275 and 5,175 Magic experience, depending on your level. (225 + 50 * level)