Posthumous Plath book (5)
I believe the answer is:
ariel
'posthumous plath book' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for ariel that I've seen before include "spirit of Shakespeare" , "Prospero's spirit (Tempest)" , "Shakespearian spirit" , "Enchanting islander" , "Free spirit" .)