Theo read the message with increasing unease and irritation. He did not take well into being threatened, and he liked even less that purchases he'd made decades ago had been recorded. It was the primary reason why he'd stopped buying illegal items (not that he'd stopped acquiring them but the people buying them for him had no clue to whom they bought the items and hence there were no trace back to him).
He knew the law well enough to know that youthful indiscretion would not send him to Azkaban if he showed that he did not have the books in his possession, but it would be enough to put a dent in his career - and that was completely unacceptable.
What was worse was that while the man again failed to write his name, Theo didn't need it to know who the sender was. His grandfather had only served one - the Dark Lord. He'd known this was going to come.
So that left the question on what to do. He could deliver the letter, hope that his services would not be needed more than that, or he could pretend to deliver the letter. Not doing it was not an option.
He did not need to think long to make his mind up, and wrote his letter back to the Dark Lord.
I will deliver Your message. Forgive me for not immediately realising that You were the sender. Threats will not be necessary in the future.
As he watched the ink disappear, he wondered if the last was wise, but only time would tell and it was not as if it would matter in the long run. The Dark Lord would not have bothered to send him a book for communication if he did not intend to use it in the future - which meant that he might as well pretend to play along, while building his defence in secret. It would be a careful balancing act, but one he was certain he'd be able to master.