Colonials thrive, unexpectedly, in 'The Scarlet Letter', say (10,5)
I believe the answer is:
historical novel
'the scarlet letter say' is the definition.
(The Scarlet Letter is an example)
'colonials thrive unexpectedly' is the wordplay.
'unexpectedly' is an anagram indicator.
'colonials'+'thrive'='colonialsthrive'
'colonialsthrive' with letters rearranged gives 'HISTORICAL NOVEL'.
'in' acts as a link.
(Other definitions for historical novel that I've seen before include "work of literature" , "work of fiction" .)