((I'm sorry for my delayed response! Holidays are busy.))
The Baron was unaware of any ancient Earth-based technology which could bend time and space. Which meant that either it had been short-lived and had been destroyed without record long ago, or this girl was from some other version of Earth which had followed a different array of possibilities along a different timeline, or, she was lying. She did not have any indications about her which suggested she lied, and it seemed unlikely that such a technology would have been destroyed.
He was curious to hear more about this technology. This girl seemed to have a decent brain, for an ancient. But, he was quite hesitant to share his discovery- still, all matters of value required exchange. And she seemed to understand this game. He nodded slightly, rumbling, "I will. But you will tell no one about this key. Or, I shall be very, ahhh, disappointed."
Operation of his suspensor device was a very subtle thing- to any casual observer it would have likely appeared that he was simply adjusting his lavish red robes, rather than engaging the harness beneath them. With this, he rose, but not to his feet- rather, he hovered ever so slightly above the ground, a reasonable setting given the limitation of train-ceilings. Me might have noticed a slight shimmer in the air surrounding him, an indication that his personal shield was also in operation, although at a low power setting. He assured they were alone in the car before drifting towards the door, where he drew his key from his robes and unlatched the lock, opening the passage upon the mostly-empty car.