The original plan was to prevent Xi Jing's mother from being taken away and to have the female detective arrest Li Chen and his men on the spot. But, upon learning who the cocktail party attendees were, Zhao Tienan decided to step into the field herself. She had a premonition that Qin Yu would eventually be taken away. Is there a quicker way to rescue Qin Yu than getting herself taken into the lair as well?
No!
So, the experienced and skilled Zhao Tienan was now "lured" into the game.
Xi Jing also chose to change her approach. She was now in too.
As their plans had suddenly changed, they didn't have time to consult each other. This lack of insight and preparation led to the current situation.
In any case, they were not exactly gaining an upper hand against Qin Yu.