This mission begins automatically after the conclusion of the previous one - To Suffer Without Dying. After Mary's death, Edward goes on a drinking binge and experiences various visions.
Edward drinks himself into a stupor, dreaming of acquiring his prize.
The first vision takes place in a tavern. Simply head toward Roberts - at the opposite end of the room.
When you get close enough for a prompt to appear, try to punch him.
You are now on the beach. All you need to do is crawl toward Roberts until you reach him.
You are now deep underwater. Simply swim all the way up to the surface.
After coming out of the water, follow Roberts and assassinate him.
Next, you need to find two more of his clones and assassinate them as well.
To help locate them, you can activate Eagle Vision.
You are now aboard your ship during a storm. Pilot the ship toward the island looming in the distance ahead of you.
Once you reach it - which will result in shipwrecking - this quest will end and the next one will be unlocked - ...Everything is Permitted.