Flighty young woman is seduced by my beloved doom-merchant! (9)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

[ Reversal of ( Flighty /taking flight?/going up, in a down clue) MISS(a young unmarried woman) + IS] contained in ( seduced by ) PET(an endearment for “my beloved”/loved one).