French tea shops tacitly involved in unmentionable work (3,8,4)

'unmentionable work' is the definition.
(superstitious name for Macbeth)

'french tea shops tacitly involved' is the wordplay.
'french tea' becomes 'the' ('tea' in French).
'involved' indicates an anagram (involved can mean confusing or complex).
'shops'+'tacitly'='shopstacitly'
'shopstacitly' anagrammed gives 'scottishplay'.
'the'+'scottishplay'='THE SCOTTISH PLAY'

'in' acts as a link.