We can’t watch, or listen, or open mail. To do any one of those things would require the resources of Esterhase’s lamplighters, and Esterhase like anyone else must be suspect. We can’t interrogate; we can’t take steps to limit a particular person’s access to delicate secrets. To do any of these things would be to run the risk of alarming the mole. It’s the oldest question of all, George. Who can spy on the spies? Who can smell out the fox without running with him?” He made an awful stab at humour: “Mole, rather,” he said, in a confiding aside.
