Outsider called, interrupting fitful rest (8)
I believe the answer is:
'outsider' is the definition.
(I've seen this before)
'called interrupting fitful rest' is the wordplay.
I cannot really understand how this works, but
'called' could be 'rang' (called on the phone) and 'rang' is found within the answer.
an anagram of 'rest' is 'ster' which is located in the left over letters.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for stranger that I've seen before include "unfamiliar figure" , "Person in place or company to which he does not belong" , "Alien; odder" , "visitor" , "More unfamiliar or odd" .)