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 am not sure about the 'classic' bit.
'armoured unit suffering with flu' is the wordplay.
'suffering with' indicates an anagram.
'armoured'+'unit'='armouredunit'
'armouredunit' with its letters 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" .)