The reason for the secret investigation was simple.
Don't startle the snake by hitting the grass.
The Fourth Prince knew she had amnesia, and Ya Fu said that all the antidotes were in the hands of the Western Region Royal Family, and without the Red Thread Worm, even Ya Fu had no way of producing an antidote.
What the Fourth Prince didn't know was how much memory he had lost and what he still remembered.
But one thing was for sure, at the time of her death in her previous life, the Fourth Prince was still alive and well.
How could she, a dead person, possibly know what happened after that?
If it weren't for that prolonged dream, she would have had no idea what happened later on.
Therefore, the Fourth Prince should guard against the things she knew while she was alive, not what happened after her death that would warrant caution.
From the fact that the two men from the trade association were not dealt with in advance, it was clear what the Fourth Prince was thinking.
