Group of five in Narnia? That's wrong (7)
I believe the answer is:
nirvana
'group' is the definition.
(US musical group)
'five in narnia? that's wrong' is the wordplay.
'five' becomes 'V' (Roman numeral).
'in' means one lot of letters goes inside another.
'that's wrong' indicates anagramming the letters.
'narnia' anagrammed gives 'nirana'.
'v' going within 'nirana' is 'NIRVANA'.
'of' is the link.
(Other definitions for nirvana that I've seen before include "State of perfect happiness" , "Transcendent state of Buddhists" , "Buddhist version of Paradise" , "Buddhist state of perfect bliss" , "religious ecstasy" .)