After his plan fell apart, Grindlewald knew he had to take revenge. It was sweet, in a way, that his favourite toy had set up house with his unmasker, but it wouldn’t do at all. So he waited until he knew that Graves had a day off from work, and that the Scamander boy had gone off on a creature hunt and let himself in.

Graves was sat at a desk, working on some paperwork, and wasn’t it pathetic that he took work home with him. Graves looked up at him and shook his head, frowning a little.
“Give me a moment.” He mumbled. “I told him he had to fix the lock.”

“Huh?” Grindlewald frowned. This wasn’t exactly the welcome he had been hoping for (that involved more tears and screaming). Graves didn’t even look particularly worried.
“Bort. I know the lock was broken, but you can’t be doing this all the time.” He frowned. “I’m working.” He reached for his wand, and took a deep breath, and if Grindlewald concentrated he could see a slight shake in his hand. There was the fear.
“Riddikulus!” He shouted, slashing his wand with the violent technique Grindlewald had struggled to echo.

It took a moment for Grindlewald to work out what was happening, but as he realised he laughed out loud, eyes shining at how perfect the situation was. He gazed straight at Graves, and shook his head slowly.
“Not a Boggart.” He said softly, his voice a purr. Graves gasped, shaking a little, and backing away, casting Riddikulus again and again. Grindlewald froze as the door opened.
“Hello.” The voice of the damn Scamander boy sounded and Grindlewald glared. He was still wearing the stupid coat he had worn on the day Grindlewald had been unmasked. “I’m going to have to ask you to leave now-“ He pulled out his wand, and Grindlewald disappeared. Graves had seen him, that would be enough for now. Especially now he knew how much Graves feared him.

Back in the house Percival and Newt shared, the figure of Newt changed into that of Grindlewald and drifted closer.
“Riddikulus!”