Im eating out with Charlie - thats mysterious! (9)
I believe the answer is:
enigmatic
'mysterious' is the definition.
(I've seen this in another clue)
'im eating out with charlie' is the wordplay.
'out with' indicates anagramming the letters (out can mean wrong or inaccurate).
'charlie' becomes 'c' (phonetic alphabet: alpha, bravo, charlie etc.).
'im'+'eating'='imeating'
'imeating' mixed up with 'c' makes 'ENIGMATIC'.
'thats' is the link.
(Other definitions for enigmatic that I've seen before include "Mystifying" , "Hard to fathom" , "not obvious" , "Difficult to interpret" , "with a mystery ingredient" .)