The most common and most likely answer to this crossword clue is the 12 letter word UNDERSTUDIES
I've seen this crossword clue in The Daily Telegraph
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More clues leading to the result UNDERSTUDIES
Buddy explains!
The straight part
We know that "They take part in emergencies" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case they take part in emergencies = understudies.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 UNDERSTUDIES mean?
UNDERSTUDIES noun- A performer who understudies; a standby.
- To study or know a role to such an extent as to be able to replace the normal performer when required.
- To act as an understudy (to someone).
- To act in a similar manner to some known person.