Back in the chamber of pain, Vinda was cackling with glee as she hit Tina with another Cruciatus Curse. Newt couldn't look. He hated seeing Tina tortured because he loved her and wanted to kiss her and do other things to her that we can't mention in a story with a "K+" rating. But when he thought about how her sacrifice would ensure that Mooncalves would be there to frolic about for future generations, he felt certain that he was making the right choice.
"Torture her all you want," he declared bravely, "but I'll still never join you!"
"You're killing me, Romeo," said Tina.
"Literally!" chuckled Vinda, raising her wand again.
But at that very moment, Credence burst into the room. "Yo, what's up?" he asked cheerfully.
"GET THE HELL OUT OF HERE, CREDENCE!" yelled Vinda, pointing her wand at him.
"Vinda!" said Grindelwald. "We don't talk that way to my asset - I mean, the son I never had." By the way, it turns out Grindelwald is a still-living Salazar Slytherin. This is canon now.
"Hey, why do you have Tina chained to that rack?" asked Credence. "Is this a game? I like games!"
"Can you make him leave?" asked Vinda, through gritted teeth.
"No, I have a better idea," said Grindelwald. "Come here, my boy."