Plug act in cape (6)
I believe the answer is:
spigot
'plug' is the definition.
(I know that spigot is a type of plug)
'act in cape' is the wordplay.
'act' becomes 'go' (go is a kind of act).
'in' is an insertion indicator.
'cape' becomes 'spit' (spit is a kind of cape).
'go' inserted within 'spit' is 'SPIGOT'.
(Other definitions for spigot that I've seen before include "Small peg or plug" , "It's a water tap in America" , "Device for stopping" , "Tap for barrel" , "Pigs to vent-peg" .)