Chapter 3: Spinner's End.
It would never occur to Narcissa that he could care about her, and about Draco, without being on the side of the Deatheaters. She was too childlike to ever understand that love, and being on the same side, were not synonymous. She knew he had loved her once, and played that card for everything it was worth.
When he forced the glass of wine into her flowerlike hand, and lowered her shaking body onto the sofa, he knew she would never guess there was veritaserum in the glass she held to her lips.
He pretended to know, but he wasn't at all sure what the plan involving Draco was. The Dark Lord really didn't trust him altogether, but liked the idea of using him to keep track of Potter and Dumbledore, since Pettigrew was altogether useless now in that regard. Pettigrew. What was he doing now, Snape wondered. Probably listening at the door. Probably scurrying back to the Dark Lord in his rat form, to report on the Unbreakable Vow Snape was taking. He hoped so.
He been ordered to prize the safety of a student, any student, over his own, or that of the Headmaster. One way or the other, Albus Dumbledore's life was over. It took every bit of his hard-won Occlumency to conceal the dismay he felt.