Talk to the Gypsy in her tent and pay her a coin to reveal the future to you. She'll do her thing and tell you that Delrith has been released. She also says that you're the only one that can stop him. She goes on into some history of Delrith, then tells you to see Sir Prysin in Varrock castle. Make sure you ask what the magical incantation is. You don't need to write it down if you're using the guide (of course). Sir Prysin is in the south west side of the castle. Ask him about Silverlight and find out he needs 3 keys to unlock the chest containing Silverlight. He'll tell you to talk to Captain Rovin on an upper floor of the castle. Go upstairs and find Captain Rovin and talk until he gives you his key. Sir Prysin dropped a key down the drain also (what a klutz), so head to the most northeast room and go upstairs, grab a bucket, go back downstairs and fill it from the sink. Use the bucket of water with the drain then hurry down into the sewers through the manhole, go a little ways in and you should find the key in no time.   Collect 25 bones and head to the Wizard Tower south of Draynor Village. Talk to the Wizard Traiborn to get your 3rd key after some mumblings about dumb stuff. Go back to Sir Prysin with all 3 keys and you get Silverlight from him at long last.
If at anytime you loose the Silverlight you can get another one by talking to Sir Prysin and by paying a 500gp fee. attack the demon till he's weak and say "Carlem Aber Camerinthum Purchai Gabindo". your quest is over =D