Slowly, Michelle developed the full antidote for the elders.
She could make it very simply, but she didn't feel like being kind to them.
So, when she finished the antidote, she made sure that the expulsion of the poison out of the elders' systems would be slow and painful.
While Michelle was doing all that (it was occupying most of her time), Vincent had to make sure the spies and elders didn't start doubting that Tobias was the culprit.
Michelle had to put her attention away from that, so it was only natural that Vincent took over.
Back when Michelle was still taking care of that, Vincent was paying attention to make sure the suspicion didn't fall upon him or anyone else.
Because, in the end, all the elders who were being targeted were from the family head's faction, so it wouldn't be hard to suspect someone from Vincent's faction.
When Michelle finally had the antidote, she warned the elders it would be a long and painful process.
