Chapter 384: Regulus Plays with the Dog [bonus]
Regulus asked without waiting for an answer. He already knew most of it.
Greyback had not been with Voldemort's camp for long. The conversation made that obvious. Every sentence had to be pried out of him. Every compromise came only after Lucius invoked the Dark Lord's name.
Greyback feared Voldemort, but there was resentment tangled up in that fear. He knew better than to defy him outright. Still, the beast in him had never accepted the idea of a master, so he haggled instead of obeying.
That told Regulus all he needed to know. Greyback was a recent recruit.
At the end of the day, he was a slightly oversized werewolf with a pack behind him. Thirty or forty wolves, perhaps. Useful to Voldemort, certainly, but not irreplaceable.
If Regulus killed him, Voldemort would be annoyed. He would not fall out with Lucius over it, and he certainly would not turn on the Black family.
So if Lucius said the Dark Lord did not care much about Greyback, Regulus could handle the wolf here and now.
Not that he actually planned to kill him.
A live Greyback was much more valuable than a dead one. The research was the point, and dead specimens were terrible at being studied.