Reward: | 3 Quest Points, Silverlight Sword

Talk to the Gypsy in Varrock town square. You need 1 coin. She will ask for silver, meaning 1 gold coin. She will explain the Delrith story and tell you to talk to Sir Prysin for the Silverlight. Ask her, "What is the magical incantation?"

Talk to Sir Prysin in Varrock Castle (north of the Gypsy). He is usually in the west wing wearing a helmet. Ask him about the keys.

Head north inside the castle and find a ladder. Go up and find Captain Rovin. Talk to him about the keys, tell him your story, and ask for the key. He will give you one.

Get a bucket (buy for 2 coins at a general store) and fill it with water. Return to Varrock Castle and use the bucket on the drain on the east side of the building. This will put a key into the sewer.

Go to the east side of the castle and enter the sewer through the manhole. Go past a level 8 rat. If there isn't one, search the area near the ladder. Look for a red dot on the map. Avoid scorpions and zombies. Grab the key.

While in the sewer, turn back towards the ladder and kill rats to collect at least 25 bones for the last key. You can bank if needed. Once you have 25 bones, head towards the Wizard's Tower (south of Draynor Village or west from Lumbridge, then south from Draynor).

Inside the Wizard's Tower, go up the first ladder. Talk to Traiborn the Wizard. He will ask for 25 bones for a spell to unlock a key. Talk to him again and give him the 25 bones, one at a time. After 25 bones, he will cast a spell and give you a key. You should now have three keys: one from Captain Rovin, one from the Varrock sewer, and one from Traiborn.

Return to Varrock Castle and talk to Sir Prysin again. Give him the three keys, and he will give you the Silverlight Sword.

Equip the Silverlight Sword and head to Delrith, located southeast of Varrock by the Stone Hedge. Attack Delrith (level 30). After a few hits, you will be prompted to say an incantation. Click the very bottom option in the spell list: "Carlem Aber Camerinthum Purchai Gabindo." Delrith will regenerate health, then it will drop to 0 again. You will be prompted for the incantation again. Click the very bottom option once more. Delrith will then die, completing the quest.