This guide is suitable for current RuneScape and Old School.
Talk to the Gossip who can be found outside the gates of the Sinclair Mansion, north of Camelot Castle.
The Gossip will tell you that King Arthur and his knights have disappeared, mysteriously the same time as the Sinclair family and you will offer to investigate further. Head through the gates and speak to the guard, however you will learn that he is afraid of losing his job and is reluctant to investigate further, and you will suggest investigating more. The doors to the mansion are locked, so head towards the east side and break through the window. Pick up the scrap paper in the northeast room, and then head upstairs and pick up the address form. Finally, search the bookcases in the same room until you find a black full helm. With these three pieces of evidence, head back and present them to the guard outside.
Investigating the Mansion
The good news is that with the evidence acquired, the guard will now be able to present the case to the Seers' Village council. The bad news is that it will take over a month to review the evidence, so naturally you will volunteer to solve the crime. The guard will suggest speaking to the Gossip again to find out some family history of the Sinclairs'. Do so, and you will learn that Anna Sinclair can be visited in the Seers' Village courthouse. Head southeast and speak to Anna, who will ask you to represent her in Court in exchange for information regarding a secret entrance into Camelot castle. Accept Anna's offer and she will give you a piece of thread and tell you to question the Sinclair servants.
Head back to the mansion and speak to the servants inside the mansion and in the garden. When you have spoken through all the options to all the servants, return back to the courthouse and climb down the stairs. Call the butler as your first witness, and speak through all the options. Call the maid as your second witness, and select the last option. Finally, call upon the dog handler and choose the third option. The jury will announce their verdict of not guilty, and Anna will then tell you to meet her inside Camelot castle, by pulling on a statue to the east of the castle. Do so, and you will learn that you have been tricked by Anna who is infact working with Morgan Le Faye. You will then be knocked out and thrown into a cell.
Escaping the Cell
When you regain consciousness, speak to Merlin to find out more about the situation you are in. You will also find out that Arthur has been turned into a statue of granite, and you will have to find a way of releasing him from the spell. When the conversations has ended, reach for the vent to make a human-ladder of knights and Merlin will climb out and escape.
Now cast telegrab on the guard outside of the jail and you will receive a hairclip. (You can also get the runes for the spell by talking to the knights in the jail). You will now have to attempt to picklock the jail door using a puzzle of tumblers. The easiest way to do this is to work methodically changing the height of the tumbler by one each time, and use trial and error to find out what works. You will get 10 tries before having to restart.
When you have escaped from the jail, you will be in Keep Le Faye. Climb to the top floor and search the long table, selecting the purple cup to rescue the holy grail. Now head to Ardougne and find Wizard Cromperty who is northeast of the market. He will tell you that to release King Arthur you will need to use another animate rock spell with added "oomph", and also a piece of granite (any weight). You must now make your way to the Black Knight's Fortress, north of Ice Mountain. Equip the iron chainbody and bronze med helm to gain entry, and then switch to the black full helm, plate and legs and push through the wall straight in front of the entrance. Climb down the ladder and free King Arthur, who will then ask you to meet him back at Camelot to claim your reward.
Congratulations! Quest Complete!
Guide Made by: DaDa
Corrections submitted by: Power of Five