The most common and most likely answer to this crossword clue is the 7 letter word CONNIVE
I've seen this crossword clue in The Guardian
C
O
N
N
I
V
E
Buddy explains!
The straight part
We know that "scheme" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case scheme = connive.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does CONNIVE mean?
CONNIVE verb- Often followed by with: to secretly cooperate with another person or persons in order to commit a crime or other wrongdoing; to collude, to conspire.
- Of parts of a plant: to be converging or in close contact; to be connivent.
- Often followed by at: to pretend to be ignorant of something in order to escape blame; to ignore or overlook a fault deliberately.
- To open and close the eyes rapidly; to wink.