I have no idea what happened with the whole almost murder thing. Someone explain?

The princess who wanted to be her ally slipped some poisonous powder into the letter she wrote to Jinsu, hence 2nd prince tearing it up and saying to clean up the mess. He was protecting our protagonist. They found out it was that princess who did that, so she was executed.

Oh... so thats what happened. I thought he magically took the dose of powder from her after possibly when he drank that little bit of milk left (￣∇￣")

And I thought the letter was just duplicated or replaced by her.