Bent on getting inside the marquee (6)
I believe the answer is:
intent
'bent on' is the definition.
'inside the marquee' is the wordplay.
'inside' becomes 'in'.
'the marquee' becomes 'tent' (I've seen this before).
'in'+'tent'='INTENT'
'getting' is the link.
(Other definitions for intent that I've seen before include "Mean to" , "Purpose under canvas" , "With attention concentrated, bent on" , "Purpose; determined" , "Design, aim" .)