The most common and most likely answer to this crossword clue is the 4 letter word PLOT
I've seen this crossword clue in The Times
P
L
O
T
More clues leading to the result PLOT
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 = plot.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 PLOT mean?
PLOT noun- (authorship) The course of a story, comprising a series of incidents which are gradually unfolded, sometimes by unexpected means.
- An area or land used for building on or planting on.
- A graph or diagram drawn by hand or produced by a mechanical or electronic device.
- A secret plan to achieve an end, the end or means usually being illegal or otherwise questionable.
- Contrivance; deep reach thought; ability to plot or intrigue.
- Participation in any stratagem or conspiracy.
- A plan; a purpose.
- To conceive (a crime, etc).
- To trace out (a graph or diagram).
- To mark (a point on a graph, chart, etc).
- To conceive a crime, misdeed, etc.