He, you and pals got involved in the theatre (9)
I believe the answer is:
playhouse
'the theatre' is the definition.
(I've seen this before)
'he you and pals got involved' is the wordplay.
'and' is a charade indicator (letters next to each other).
'got involved' indicates anagramming the letters.
'he'+'you'='heyou'
'heyou' after 'pals' is 'palsheyou'.
'palsheyou' is an anagram of 'PLAYHOUSE'.
'in' acts as a link.
(Other definitions for playhouse that I've seen before include "Stage" , "army theatre" .)