Classic story of armoured unit suffering with flu (3,6,6)
I believe the answer is:
our mutual friend
'classic story' is the definition.
'our mutual friend' can be an answer for 'story' (Charles Dickens novel). I'm not certain of the 'classic' bit.
'armoured unit suffering with flu' is the wordplay.
'suffering with' indicates an anagram.
'armoured'+'unit'='armouredunit'
'armouredunit' anagrammed with 'flu' makes 'OUR MUTUAL FRIEND'.
'of' acts as a link.
Can you help me to learn more?
(Other definitions for our mutual friend that I've seen before include "Novel" , "John Harmon" , "you and I know and like" , "China we share" , "someone we both know" .)