Keep hidden blue story with position-swapping (3,3)
I believe the answer is:
lie low
'keep hidden' is the definition.
(I've seen this before)
'blue story with position-swapping' is the wordplay.
I cannot quite see how this works, but
'blue' could be 'low' (both can mean sad) and 'low' is present in the answer.
'story' could be 'lie' (story can mean a fabrication) and 'lie' is found within the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for lie low that I've seen before include "Keep hidden" , "Conceal oneself in recumbent posture?" , "Go into hiding" , "Go to ground" , "Avoid attracting notice" .)