It's time to kill...It's time to Insta-Kill!

Start
When you search the sacks near the bank on the top floor of Lumbridge Castle you will find a bottle of Insta-kill and a note.

The note
The note says that a professor named Dr. A Yankovich that concocted a bottle that, when fed to a creature that is of combat level 150 or less, will kill it instantly. On the bottom of the note it explains that he keeps creatures and his laboratory in Death Caverns, and it will have a pass for the next person who read the note to Death Caverns. Death Caverns, it will say, is in the nearest church to a city for the dead come alive. That means where the dead come back alive, which is most commonly Lumbridge.

Death Caverns
Death Caverns is accessible by using a Mithril pickaxe or better on one of the benches in the church. This will require level 40 Mining. Father Aereck will run over to you and ask what you are doing. Tell him you have a pass and he will let you in. In the Caverns, you will notice Rune dragons to the north and east. Go west and you will find a lever. Pull the lever and you will fall through a trapdoor. You may get damaged if you are Defence level 35 or lower. When you reach the bottom, you will find the laboratory.

The Lab
The lab would abandoned at first sight, but if you follow the trail of bones to the other room, you will find a Rune dragon in a cage. On the west you will see a cracked wall. Use your pickaxe it. On the floor, you will see dust and a key. Use the key on the cage with the Rune dragon. Make sure you have good armour and the Anti-dragon shield (g). Once the dragon has less than half health, use the Insta-kill on it. Once you defeat the dragon, you will complete the quest.

Rewards

 * 13,000 coins
 * Access to the Death Caverns to fight the most anticipated Rune dragon
 * Access to the Death Caverns to fight the most anticipated Rune dragon
 * Access to the Death Caverns to fight the most anticipated Rune dragon
 * Access to the Death Caverns to fight the most anticipated Rune dragon