Tell some strange tale, rather upsetting (6)
I believe the answer is:
relate
'tell' is the definition.
(as in to tell or relate a story)
'some strange tale rather upsetting' is the wordplay.
'some' indicates a hidden word (some parts of the word are used).
'upsetting' shows that the letters should be reversed in order.
'etaler' is hidden in the letters of 'strange tale rather'.
'etaler' back-to-front is 'RELATE'.
(Other definitions for relate that I've seen before include "Marriage Guidance - report" , "Give a report or show a connection" , "Do well; wave about" , "Tell; a counselling service" , "Narrate or connect things" .)