Merlin's Crystal/Quick guide

Getting started

 * Talk to King Arthur about joining the round table
 * Ask Sir Gawain nearby about how Merlin got trapped
 * Talk to Sir Lancelot upstairs about the stronghold
 * Go to Catherby docks and talk to Arhein about riding his ship
 * Hide in the crate north of the candle-maker

Inside the keep

 * Climb to the top floor
 * Attack Sir Mordred
 * Spare his life to discover how to save merlin
 * Exit the keep and kill a bat if you don't already have bat bones

Black candle

 * Talk to the candle-maker in Catherby about black candles
 * Take the insect repellent from the house north of the bank
 * Run west to the bee hives
 * Take the bucket
 * Use the insect repellent on any bee hive
 * Use the bucket on the same hive
 * Return to the candle-maker

Excalibur

 * Talk to the lady of the lake in southern Taverly
 * Teleport to Port Sarim
 * Buy a loaf of bread from the food shop
 * Enter the jewelry store to the north
 * Give the beggar your bread

Ritual

 * Go to the Zamorakian temple in south-west Varrock
 * Check the chaos altar's inscription
 * Return to Camelot and enter the gates
 * Run East of the castle to the ritual site
 * Stand on the star
 * Light the black candle
 * Drop the bat bones on the star
 * The magic words are "Snarthon Candtrick Termanto"

Finishing up

 * Enter the castle and climb the south-east tower
 * Smash Merlin
 * Talk to King Arthur
 * Quest complete!