The most common and most likely answer to this crossword clue is the 9 letter word FLOWCHART
I've seen this crossword clue in The Times
F
L
O
W
C
H
A
R
T
More clues leading to the result FLOWCHART
Buddy explains!

The straight part
We know that "plan of work" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case plan of work = flowchart.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 FLOWCHART mean?
FLOWCHART noun- A schematic representation of how the different stages in a process are interconnected.