"I'm larger and stronger than she is, and I have magic that made it easier."
I can also gain physical or magical abilities by killing people who currently have them, but it's inefficient."
It's true. He's well and truly trapped.
"Promise. She used to be a vassal of yours before you sold her."
"Her subsequent master captured me. We escaped together by each vassaling the other, and I gained control by commanding her to take no new action."
"I would need to go back to my world, open a particular door a particular way in case she's watching, and find her to give an order."
Alendi's reaction is less despair than it is "Oh, that's how that happened." Then despair.
"I'm only unpleasant if you make me that way," purrs Thorn. "Blossom likes me quite well, for example. Promise, by contrast, was scarcely worth the trouble it took to take her, but now she's sent me you, which might make up for all her... misbehavior. I don't advise misbehavior," Thorn adds. "I haven't had a mortal in a while, let alone a dubiously mortal one, and for all I know if you make me punish you I'll overshoot and you'll die incapable of screaming on my floor and I'll have to console myself with a much better pleased Blossom and Verve. Tell me what you're thinking."
Really, what else could he be thinking after that?
"Stand up. In general, if you form any intention to do anything that seems like it might in my opinion constitute a loophole, an exploitation, or a violation of my desires, bite off your tongue and calculate the cube roots of the numbers between one trillion and ten trillion by brute force until further notice from me. Follow me."
Thorn leads him out of the library.
They are joined by a short red and yellow fairy. "Master," this fairy says to Thorn.
"Yes, Twirl?"
"Rainfall says she wasn't taken."
Thorn looks over his shoulder at Alendi. "Did you get your captive's nickname wrong, Alendi?"