She's beginning to suspect vicious men affected rascal's behaviour (15)

I believe the answer is:

mischievousness

I'm a little stuck... Click here to teach me more about this clue!

'rascal's behaviour' is the definition.
The definition and answer can be both acts as well as being singular nouns.
Perhaps there's a link between them I don't understand?

'she's beginning to suspect vicious men affected' is the wordplay.
'beginning to' indicates taking the first letters.
'affected' indicates anagramming the letters.
The first letter of 'suspect' is 's'.
'shes'+'s'+'vicious'+'men'='shessviciousmen'
'shessviciousmen' is an anagram of 'MISCHIEVOUSNESS'.

Can you help me to learn more?

(Another definition for mischievousness that I've seen is " devilment".)

I've seen this clue in The Independent.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.