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

1.
挺身而出, 填补空缺
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.
当主角生病时,他的替补不得不挺身而出。
•
The volunteers had to step into the breach when the regular staff went on strike.
当正式员工罢工时,志愿者不得不挺身而出。