[lǐ gōu wài lián]   

里    勾    外    连    内外勾结，串通一气。

释义：内外勾结，串通一气。出处：明·施耐庵《水浒》第六十二回

Act from inside in coordination with forces attacking from outside

里勾外连    里外夹攻    里丑捧心    里应外合    里出外进