Girl arrested at Stonehenge starts to excavate some stones (4)
I believe the answer is:
tess
'girl arrested at stonehenge' is the definition.
(reference to the novel Tess of the d'Urbervilles)
'starts to excavate some stones' is the wordplay.
'starts' says to take the initial letters.
The first letters of 'to excavate some stones' is 'TESS'.
(Other definitions for tess that I've seen before include "Lady" , "Ill-starred Hardy heroine" , "'Justice' finally done on her (Hardy)" , "Hardy's pure woman" , "Hardy's Durbeyfield heroine" .)