흑막이 · 흑막을
hidden scheme, behind-the-scenes intrigue, dark secret
Example
이번 비리 사건에는 큰 흑막이 숨어 있는 것 같아요.
It seems there's a big hidden scheme behind this corruption case.
Word parts
흑 black+막 curtain
Literally 'black curtain' — what's hidden behind it.
Good to know
Pronounced [흥막] — nasalization.