Deliver mislaid cases Spain delivered (8)
I believe the answer is:
relieved
'delivered' is the definition.
(relieving is a kind of delivering)
'deliver mislaid cases spain' is the wordplay.
'mislaid' indicates an anagram.
'cases' is an insertion indicator (forms a case around).
'spain' becomes 'e' (abbreviation for Espana).
'deliver' with letters rearranged gives 'relived'.
'relived' placed around 'e' is 'RELIEVED'.
(Other definitions for relieved that I've seen before include "Made less monotonous" , "Freed from distress" , "'Alleviated, lightened (8)'" , "Alleviated, eased" , "Replaced on duty" .)