to become involved in a difficult situation or argument in order to help find a solution插手;介入;居中斡旋
[ + to infinitive ] An outside buyer has stepped in to save the company from going out of business.一个外来买主介入,使公司免于破产。 When the leading actress broke her leg, Isobel stepped in and took over.女主角摔断了腿,伊索贝尔临时加入顶替了她。