Prosecute stalker? Essentially that's most appealing (6)
I believe the answer is:
cutest
'most appealing' is the definition.
(I've seen this before)
'prosecute stalker? essentially' is the wordplay.
'essentially' says the answer is hidden in the clue (essence can mean the inside of something).
'CUTEST' is hidden in the letters of 'prosecute stalker'.
'that's' acts as a link.
(Other definitions for cutest that I've seen before include "Most sweet and endearing" , "Smartest" , "Most appealing" , "Most pretty" , "Most clever" .)