Snape allowed a flicker of alarm onto his face. "You won't want to hear me say this," he said quietly, "but knowing Riddle as I do, the most likely possibility is that he has already thoroughly subverted one or both of them; he intends to use them against us: as assassins, or deep cover agents, or both."
He drew a deep breath. "Even if I'm wrong, they will of course require thorough testing. I shall have to gather certain pieces of equipment and conduct other preparations. Thank you for the advance warning," he concluded briskly, "I shall ensure that everything is ready to go with me when the Ministry calls tomorrow night."