The boy nods and shuts the door.  As they're leaving, they can hear him talking to his friends: "Don't know why they're bothering, if my mum'd gotten me a toad I'd lose it as fast as I could.  Mind you, I got Scabbers..."

- Wow what a jerk.

She nudges Neville. "We'll keep looking. Bet Trevor's found a ton of candy crickets or something."

"That boy seemed terribly rude to me," Hermione says.  "I doubt he'd have been much help anyway."

Small smile.

She nods, seriously. "We'll find someone nicer and helpful."

Hermione frowns pensively.  "Actually, I wonder if it might be best to go looking for a prefect.  They might be able to cast a scrying-spell that could find Trevor more easily than just checking manually.  And I suppose if someone found him, the prefect's car would be where they'd take him."

"Oh, that's a good idea! Do you know where they are?"

"There's a prefects-only car in the front of the train," Hermione says.  "At least some of them should be there, I think."

" - And we've been walking back..."

"We'll just have to backtrack," Hermione says.  "We haven't gone too far."

She nods. "Yeah."

So off they march, back toward the front of the train.

Harriet knocks when they get to the prefect's compartment.

The door slides open, and reveals a woman (or at least a girl a good few years older than them) in blue-trimmed robes.  "Can I help you?" she asks.

"Uh, maybe," she says. "Neville lost his toad, Trevor, and we haven't been able to find him..."

"Oh dear," the prefect says.  "Well, no one's come by with a lost toad today, but I might be able to try a scry... do you have anything he's touched?  Were you holding him with your bare hands recently?"

Neville holds out his hand...

...and the prefect presses the tip of her wand to a few spots, in sequence, frowning pensively.  After a moment, she raises her wand up, and a little glinting point of blue-white light forms on the tip.  She taps her wand smartly with one finger, and the light-droplet hops off her wand and swoops out the door and down the hall.

"That should be back in a minute or two," she says.  "You can wait here, if you'd like."

Harriet nods. "I'm okay waiting."

"So am I."

Neville nods.

And, not even a minute later, the blob returns - 

Followed immediately by a knock on the prefects' compartment's door.

Prefect pokes the point of light out of the air with her wand, and makes a face like trying to blink away a bright afterimage; and then smiles, and opens the door.

There is:

A boy, about the same age as Harriet and her friends, firmly holding: Trevor!

"I found this toad..." he says, holding up his cargo. "I think he belongs to someone..."