Frenchman in scientist's place of work is one of Mary's followers (4)
I believe the answer is:
lamb
'work is one of mary's followers' is the definition.
I can't judge whether this defines the answer.
'frenchman in scientist's place' is the wordplay.
'frenchman' becomes 'm' (abbreviation for Monsieur - like 'Mr').
'in' is an insertion indicator.
'scientist's place' becomes 'lab' (I am not sure about this - if you are sure you should believe this answer much more).
'm' placed within 'lab' is 'LAMB'.
'of' is the link.
Can you help me to learn more?
(Other definitions for lamb that I've seen before include "Exemplar of innocence" , "Agnus Dei - . . . . of God" , "Young sheep" , "Young shee" , "author?" .)