The most common and most likely answer to this crossword clue is the 3 plus 5 plus 2 plus 4 letter word ALL HANDS ON DECK
I've seen this crossword clue in The Times
A
L
L
H
A
N
D
S
O
N
D
E
C
K
More clues leading to the result ALL HANDS ON DECK
Buddy explains!

The straight part
We know that "everyone must get involved" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case everyone must get involved = all hands on deck.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.