The most common and most likely answer to this crossword clue is the 9 letter word SPYMASTER
S
P
Y
M
A
S
T
E
R
More clues leading to the result SPYMASTER
- Discover M has plant for top agent?
- This could be M’s part? Yes
- Francis Pym: a sterling host for the head of 6?
- Second bloomer overwhelms Pym, or M?
- Messy part upset M, say
- One has agents sorting out party mess
- Someone having agents to sort out party mess
- Mess party organised by M, for example
- Employer of agents unusually smart, yes? Must keep quiet!
Buddy explains!

The straight part
We know that "M, say" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case m, say = spymaster.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 SPYMASTER mean?
SPYMASTER noun- The leader of a group of spies.