It pleased Severus to see that Lucius still felt he was worthy of his time. This was someone that recognized his worth, his skills.
"Indeed," he said. "One must know always exactly whom one is dealing with." He wouldn't say he trusted Lucius completely, but if there was anyone he did, it was this man.
He still needed to go back and get his book, but he nodded in agreement. "I'm glad we spoke as well." He nodded sharply at the other man's compliment. "And you are too kind." His lips curved up at the corners. "Honest and perceptive. But kind."