the_debt_of_time

"Because we thought that you either were or knew who the heir of Slytherin was,
so Harry and Ron Polyjuiced themselves into Crabbe and Goyle and sneaked into the
Slytherin common room to question you," Hermione blurted out and then immediately
covered her mouth, eyes wide.
"And I'm the untrustworthy one?" Draco scoffed. "All right, Black, let's get this over
with before it wears off. But at the end of this war, I've got some bloody questions of my
own," he said, pointing to Hermione and Harry, purposely ignoring Ron who still kept his
wand trained on him.
"All right, who holds your loyalty?" Sirius asked Draco.
"My mother," Draco said at once.
"Not Death Eaters?"
"No," Draco insisted.
"Are you a Death Eater?"
"Technically," he said through clenched teeth.
"You said you were on our side. How so?"
"At the end of fourth year, I was recruited as a spy because it was assumed that I
would be pulled into the Death Eater ranks because of my father. Therefore, I was deemed
a valuable asset," Draco explained. "I've been watching, passing information, and helping
the Order ever since."
"Who recruited you?" Sirius asked.
"Severus Snape."
"Let me hex him!" Ron shouted angrily.
"Severus Snape is a bloody traitor!" Sirius growled. "He murdered Dumbledore!"
"No." Draco shook his head. "I don't know all the details, but I was told that Snape
and Dumbledore had some arrangement. After I was instructed to kill Dumbledore myself,
Snape took me aside and told me to fulfil the mission as completely as possible with the
exception of actually killing Dumbledore. I was to disarm him and wait for Snape to show
up. I didn't know he was going to kill him."
"He's telling the truth," Hermione said.
"Even if Snape did betray your precious Order, I haven't," Draco insisted.
"Prove it," Ron demanded.
"Prove it? I'm under Veritaserum, you fucking idiot."