Wreck of Crete in Steamship Mysteries (7)
I believe the answer is:
secrets
'mysteries' is the definition.
(I've seen this in another clue)
'wreck of crete in steamship' is the wordplay.
'wreck of' is an anagram indicator (I've seen 'wrecks' mean this).
'in' indicates putting letters inside.
'steamship' becomes 'ss' (nautical abbreviation).
'crete' is an anagram of 'ecret'.
'ecret' going into 'ss' is 'SECRETS'.
(Other definitions for secrets that I've seen before include "Undivulged facts" , "Concealed facts" , "Hidden facts" , "Confidential matters" , "Mysteries" .)