Harper: I came to deliver a message from Ben. The two people you're looking for, they're headed to the Tempest. And if they figure out how to deploy that gas, then everyone on the island is going to die.
Juliet: Why don't you stop them?
Harper: Because Ben wants you to go.
Juliet: How does Ben know where they are if he's prisoner?
Harper: Ben is exactly where he wants to be.