step into the breach
US /stɛp ˈɪntu ðə briːtʃ/
UK /stɛp ˈɪntu ðə briːtʃ/

1.
挺身而出, 填補空缺
to take action when another person or group is unable to, or to fill a gap in a difficult situation
:
•
When the lead actor fell ill, his understudy had to step into the breach.
當主角生病時,他的替補不得不挺身而出。
•
The volunteers had to step into the breach when the regular staff went on strike.
當正式員工罷工時,志願者不得不挺身而出。