【投井下石】〖tóu jng xià shí〗[throw stones at sb. who has fallen into a well -- to hit sb. when he's down; attack sb. who has already fallen from power; push sb. down a well and then drop rocks on him]

投隙抵罅乘危急，

井栏提桶坠水里。

下怀正中加陷害，

石火电光落砸死。

比喻乘人危急的时候，加以陷害。Metaphor at person  in desperate situation time, implement frame-up. 同：落井下石。