In the Daqian Dynasty, there were aftermaths of seizing the legitimate heirs within, and there were Beidi cavalry looking at them from outside. The emperor was old and suspicious, and there were constant factional disputes in the court.
The prince who was the most "sick young man" in the court was forced to marry the princess who was the most "female murderer" in the enemy country.
On the wedding night, both of them were preparing to assassinate each other, but found that the other's skills seemed... A little too good?