Power left in the grip of lessees, terribly disturbed? (9)
I believe the answer is:
sleepless
'disturbed?' is the definition.
(thesaurus)
'power left in the grip of lessees terribly' is the wordplay.
'power' becomes 'p'.
'left' becomes 'l' (common abbreviation).
'in the grip of' means one lot of letters goes inside another.
'terribly' is an anagram indicator.
'p'+'l'='pl'
'lessees' with letters rearranged gives 'sleeess'.
'pl' put within 'sleeess' is 'SLEEPLESS'.
(Other definitions for sleepless that I've seen before include "Suffering from insomnia, not in the land of Nod" , "Insomniac" , "Film: '-- in Seattle'" .)