The Dementors ignored him and continued "feeding" as they searched for Sirius. Professor Lupin sighed.
His position was unusual, and it wouldn't do for him to get into too many conflicts with Ministry of Magic employees.
But he was a professor now, and one of his students was in danger.
Professor Lupin raised his wand and canceled the Sonorus Charm attached to his throat.
A faint silver light gathered at the tip of his wand as he pointed it at the Dementors.
"One last warning. If you don't stop harming the young wizards, I'll have no choice but to..."
"Expecto Patronum!"
A clear voice rang through the entire train, replacing Professor Lupin's. A mass of silver light flew out and took shape in front of him.
A silver Medusa stood in the train corridor, gazing impassively at the Dementors.
The snake heads at the tips of her many serpents rose as well. They hissed and stared at the Dementors.
"Drive them out," Harley's cool voice echoed through the train again.
Medusa's serpents lunged at the Dementors, slamming them hard against the floor.
At the same time, a brighter silver light burst from her, warm and radiant, dispelling the darkness and cold around them.
Under Harley's control, Medusa's mass of serpents grew longer and longer, driving every Dementor from the train.
Harley's voice rang out beyond the train as well.
"The Dementors actually dared to attack a professor, and even tried to give an innocent young wizard the Dementor's Kiss!
"I'll tell Headmaster Dumbledore and Minister Fudge about this, and expose how you tried to harm students and conspired to destroy the future of the Wizarding World!"
The lights on the train came back on. As the storm raged, it slowly started moving again, heading toward Hogwarts Castle and leaving the