Simply seething like some boys in trouble (5)
I believe the answer is:
aboil
'simply seething' is the definition.
'aboil' can be an answer for 'seething' (I've seen this in another clue). I'm unsure of the 'simply' bit.
'like some boys in trouble' is the wordplay.
'like some boys' becomes 'bo' (I can't explain this - if you can you should give a lot more credence to this answer).
'in' is an insertion indicator.
'trouble' becomes 'ail' (synonyms).
'bo' going inside 'ail' is 'ABOIL'.
Can you help me to learn more?
(Another definition for aboil that I've seen is " seething".)