After the takeover Theo found reasons to be downstairs more often than not. The first floor was littered with people like the Lestranges and Greyback and the Dark Lord and the less he saw of them the better. It was fortunate that he had already years ago arranged for a second office closer to the Department, as to better oversee what they did.
When the Dark Lord came down he wasn't in his office, however, but talking to an employee. He turned instantly, bowing his head in greeting - and in a way, submission - though he hated the very idea. "Sir," he replied.
"We've made some progress," Theo answered. "Though our job has been made more difficult now that we no longer have access to Hogwarts," he said. "We've also lost two of those who had worked on this the longest, which is a setback, though not an insurmountable one," he hastened to add. Truth was that they only had theories, and none of them could be tested without access to Hogwarts, but he wasn't about to tell the Dark Lord that.
"We have an office set up for the research if you'd like to see it," he offered. "Right now our best bet is that we're dealing with ancient magic, but we aren't closing any avenues before we have evidence one way or another."