Tian , however , persuaded Li Baochen to turn against Zhu .
Late in 775 , Li Baochen launched a surprise attack on Zhu 's army and then attacked north , hoping to capture Lulong 's headquarters .
Tian , however , persuaded Li Baochen to turn against Zhu , and late in 775 , Li Baochen launched a surprise attack on Zhu 's army and then attacked north , hoping to capture Lulong 's headquarters .