hole-and-corner

Hole-and-corner describes something done secretly or furtively, often with implications of being underhanded or not quite legitimate.

The phrase evokes the image of someone conducting business in hidden spaces away from public view.

The whole thing had a hole-and-corner quality that made me suspicious.

It's more common in British English and carries a slightly old-fashioned flavor, often applied to clandestine meetings, shady dealings, or anything that seems deliberately kept from scrutiny.