Assassin's Creed IV: Steal the warehouse key

Steal the key in AC4 Black Flag

"Steal the key" is a mission objective in Sequence 3 / Memory 05: Sugarcane and its Yields

Walkthrough

Try assassinating the key holder from the Stalking Zone

Or you could just kill him in the open and get the key from his dead body

Next objective

Loot the warehouse