Brilliant escape by criminal (7)
I believe the answer is:
lambent
'brilliant' is the definition.
(I've seen this before)
'escape by criminal' is the wordplay.
'escape' becomes 'lam' (lam is a kind of escape).
'by' means one lot of letters go next to another.
'criminal' becomes 'bent' (I've seen this before).
'lam'+'bent'='LAMBENT'
(Other definitions for lambent that I've seen before include "Brilliant and light of wit" , "shedding some light" , "Shining example" , "Of flame or light, playing about a surface" , "inflamed?" .)