Grindelwald and Vinda brought Newt and Tina into the chamber of pain, which was a chamber in which pain occurred. That would be a good thing if the pain was going to be done to Grindelwald and Vinda, who definitely deserved it, but instead, it was going to be inflicted on our gallant heroes!
By the way, it turns out even Grindelwald wasn't evil enough to not wash his hands after going to the bathroom. This is canon now.
"Go ahead and torture me to death!" Newt declared stoutheartedly. "I'll never join you!"
"But it's not you who will be tortured to death," said Grindelwald, grinning iniquitously. "It's your girlfriend." And with that, he pointed his wand at Tina!
Newt gasped. "She's not my girlfriend!" he exclaimed indignantly.
"Definitely not!" Tina agreed.
"I'm sorry, did we catch you between one of your numerous break-ups?" asked Grindelwald perniciously.
"We haven't broken up that often!" Newt replied. "Just... seven times over... the past three months..."
"It's eight times, actually," said Tina.
"No, it's seven. That polka incident doesn't count."
"Well, I think it should count."
"ENOUGH!" roared Grindelwald. "The point is, either she dies or you help us!"
"If you're asking me to choose between fantastic beasts and the woman I love," said Newt, "then I choose the beasts!"