Telltale creep (5)
I believe the answer is:
sneak
I believe this is a double definition.
'telltale' is the first definition.
(I've seen this before)
'creep' is the second definition.
('sneak' can be a synonym of 'creep')
(Other definitions for sneak that I've seen before include "Go furtively - inform on another child" , "Petty informer" , "thief" , "Prowl" , "Snitcher" .)