The next place you need to go is the Monastery. It is located east of Ice Mountain. When you reach it, go north and you will see some Cabbages. Pick one up.

Now it's time to start your mission. Go to the Black Knights Fortress which is located on the north side of Ice Mountain by your . If you have the Bronze medium helmet and the Iron chainmail right now, wear them and take your . After putting them on, open the sturdy door in the central part of the fortress, facing the south. Push the wall just behind the door and go up the ladder. Once inside, you can put your normal (stronger) armor on for extra defence.

After you push the wall, climb the 2 ladders to get to the top floor. Climb down the ladder on your southeast side. Open the door on your east side. Open the other door and climb up the ladder. This room has two cannons and a Black knight. Climb down the ladder on your east side. You will be now in a room with a Zamorak altar. Open the door and a Black knight will attack you. Either kill him or ignore him, then keep going. Climb the ladder on your southwest. Now you will be in a small room.

Now we will start spying. Click the option on Listen-at grill. The witch will say that the secret weapon is almost ready. She will need the last ingredient which is a Cabbage that grew in Draynor Manor. She will say that if the goblin fetches the wrong Cabbage, the secret weapon will be destroyed. That's your way to destroy the weapon!

Go back downstairs to the main floor and push the wall. Now it's time to open the door on your east. One of the guards will say that the Black knights are having an important meeting and they will kill everyone who gets in. Say that you are brave and go in. One of the Black knights will attack you. Either kill him or go up the ladder. Walk east and south and push the wall. You will see a hole. Remember the Cabbage you picked? Use that Cabbage on the hole. The Cabbage will fall into the cauldron and destroy the weapon. Now your job is done.

Go back and talk to Sir Amik Varze. He will reward you.