Possessions of saints in the mysterious East (6)
I believe the answer is:
assets
'possessions' is the definition.
(asset is a kind of possession)
'saints in the mysterious east' is the wordplay.
'saints' becomes 'ss' (an abbreviation for saint written twice).
'in' is an insertion indicator.
'the mysterious' is an anagram indicator.
'east' anagrammed gives 'aets'.
'ss' going within 'aets' is 'ASSETS'.
'of' is the link.
(Other definitions for assets that I've seen before include "Advantages" , "Total value of possessions" , "Valuable property" , "One's valuable possessions" , "Properties that have money value" .)