Devious Minds

Talk to the monk outside Paterdomus Temple, north-east of Varrock. He wants a weapon built from an eastern design.

• Bow string

Use the mithril two-handed sword on the whetstone inside Doric's house north of Falador to make a slender blade, then attach a bow string to make the bow-sword.

Take it back to the monk. The balloon from Taverley to the Earth Altar is the quick route if you have unlocked it.

The monk asks you to deliver an orb to Entrana for a ceremony, hidden inside an essence pouch and carried through the Abyss to the Law Altar.

Only a large or colossal pouch works, and it must not be degraded. The large pouch is destroyed during the quest; a colossal one survives. Repair it with the dark mage first if needed.

Take the Abyss route to the Law Altar on Entrana, since the monks would never let you land with the orb by boat.

Use the pouch on the altar in the church at the centre of the island. A cutscene plays: an assassin with the bow-sword teleports in, kills the monks and takes the relic.

Talk to the High Priest afterwards. The orb was a teleport beacon, and both the weapon and the way in were your doing.