“Of course he told you that, ” said Harry, “but he was Dumbledore's spy from the moment you threatened her, and he's been working against you ever since! Dumbledore was already dying when Snape finished him! ”
Plainly, each of these expressions meant something secret, and Frank could think of only two sorts of people who would speak in code: spies and criminals.
" He's a spy sent to keep us in view! That isn't quite the thing, either, to be spying Mr. Fogg, who is so honourable a man! Ah, gentlemen of the Reform, this shall cost you dear" !
He had been their spy, Dumbledore had said so in the Pensieve. Snape had turned spy against Voldemort, " at great personal risk." Was that the job he had taken up again?