Happy Never After
It was a stark promise, and Derek always fulfilled his promises. He would break her walls of defense until there was nowhere left for her to shield her emotions any longer. Lay bare her vulnerability and let her be destroyed by her own fears, just like she did to him today.
Derek was one who held grudges deeply, bounding it round his girdle like a garment, thus, even though what Rain had disclosed about him earlier was of no use, he would certainly get back on her for it.
And since she'd made the personal choice to be a hostage, he owed her no favors or humanly treatment.
Henceforth, her duty would be to simply suffer repercussions for the sake of her 'charming savior.'
On the contrary, her misery would've been lessened if he had obtained her like his previous plan.