Fools one doctor taking back diamonds by the French (9)

'fools one doctor' is the definition.
I can't tell whether this definition defines the answer.

'back diamonds by the french' is the wordplay.
'back' says the letters should be written backwards.
'diamonds' becomes 'ice' (slang term for diamonds).
'by' becomes 'bmi' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'the french' becomes 'les' (plural form of 'the' in French).
'ice'+'bmi'='icebmi'
'icebmi' backwards is 'imbeci'.
'imbeci'+'les'='IMBECILES'

'taking' is the link.

Can you help me to learn more?