The most common and most likely answer to this crossword clue is the 13 letter word MASTERMINDING
I've seen this crossword clue in The Times
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More clues leading to the result MASTERMINDING
Buddy explains!

The straight part
We know that "Planning" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case planning = masterminding.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 MASTERMINDING mean?
MASTERMINDING verb- To act in the role of mastermind.
- A creativity technique by which a group tries to find solutions for a specific problem from ideas spontaneously contributed by its members.