将计就计

jǐng fāng qīng chu tā men bì xū jiāng jì jiù jì cái néng dǎi zhù nà ge shā rén xiōng shǒu

警方清楚他们必须将计就计才能逮住那个杀人凶手。

The police knew that to trap the killer they had to play him at his own game.