Clue: 51 first-rate lads corrupt grandee employs in 13 novel (8,11)
Answer: LIAISONS DANGEREUSES
Explanation: Definition: 13 novel
LI (51) + A1 SONS + GRANDEE* + USES. To be picky, the name of the epistolary novel (made ino a memorable 1988 film, among other adaptations) is *$$Les$$ Liaisons dangereuses