Broken heads in the underworld (5)
I believe the answer is:
hades
'underworld' is the definition.
(Hades can mean the underworld in Greek myth)
'broken heads' is the wordplay.
'broken' indicates anagramming the letters.
'heads' with letters rearranged gives 'HADES'.
'in the' acts as a link.
(Other definitions for hades that I've seen before include "The nether world, hell" , "It's classical hell in the shade" , "Home of the souls of the dead" , "Greek god of the underworld" , "Pluto" .)