He raised his wand slightly when her hand went to her wand, knowing that James was likely doing the same thing. When she turned her hair pink though, he frowned.
"And being a metamorphagus means that you can take on Tonks' appearance and pretend to be returned from the dead. We all know magic doesn't work that way. You don't return from the dead and think it's 26 years ago." Though damn if she was not a good actress. He prided himself on being able to spot lies a million miles away, and she was as good a liar as he himself was. He couldn't spot a single tell.
Had he not known it was impossible he would have sworn she was telling the truth.
"In here," he said, opening a door to a classroom. James went in first, he then waited for 'Tonks' to follow before he entered himself. "I would be much more at ease if you either handed over your wand or placed it on the table over there," he said nodding towards a table in the corner of the room.
He pondered for a moment asking James to contact Tonks' son to prove that she wasn't who she claimed to be, but really it would be foolish and cruel to rouse him in the middle of the night for something that was obviously a hoax. Instead he addressed James, not taking his eyes off Tonks.
"Go and find the potions teacher," he said. "See if they have any veritaserum, if not make sure they bring some from the ministry."
"If you are who you say you are you should not be opposed to taking it, should you?" he then said to the imposter. "Or you might spare us the trouble and start to tell the truth." From the corner of his eye he could see James exiting the room.
"Why don't we start with your name, your real name."