Nor could it be therein? (7)
I believe the answer is:
neither
'nor could it' is the definition.
I can't tell whether this defines the answer.
'therein?' is the wordplay.
'therein' anagrams to 'NEITHER'.
But, I am unsure how this is indicated.
'be' acts as a link.
Can you help me to learn more?
(Other definitions for neither that I've seen before include "Not one of two" , "None of the two" , "Negative word" , "And not; nor yet" , "Therein lies not one or the other" .)