Ron's body bucked and Harry barely managed to maintain the connection between them. He felt rather than heard Hermione cast an Immobulus, which slowed Ron down without locking his body up altogether. He began tearing at the blackness with his mind, trying to dig a hole through Grindelwald to Ron, but it was like tearing tissue paper off an endless roll.
Ron, I'm not leaving, but your body- I don't have a lot of time. You have to help me!
Harry could feel Grindelwald's vile mind closing in on him from all sides, and Ron's pleading voice was barely the ghost of a whisper.
"We'll never let you have him! We love him! We'll never stop until he's returned to us!" At this point, though, Harry felt like he was running on pure bravado. He could hear Snape now, laughing at him, and Harry had to chase his doubts away again.