The boy in the train compartment is a Muggle. They likely don't even speak the same languages. This suits Tom's purposes beautifully.

He makes the first overture by way of an apple. Salazar's ring sits heavy on his finger and it seems like a delightful jest. Glistening red from English shores, enchanted for freshness and to weather a journey in a coat-pocket but otherwise quite ordinary. The boy in his grey overcoat strikes it from his hand and catches it, glowering like a dog. He is dirty in comparison to Tom's scrubbed Englishness and his cropped hair makes him look institutional. Even in receiving a handout he's ungrateful. Suspicious. Tom settles back, crossing his legs.

Such a strange, sallow face. He has not said a whole word the whole journey, not a word to himself or in greeting, not a muttered profanity. Maybe he's a mute. Perhaps -- Tom has a brief flight of fancy about the boy's tongue being cut out by Nazi soldiers. He can picture it very well, and it's not a scene without charms. Limbs splayed, one uniformed man to hold him fast and the other to force his jaw down, part those red lips, cut a red swathe behind white teeth. It's very erotic, but the allure is punctured by watching the boy begin to eat. The boy devours Tom's gift, tearing at the ruby skin ruthlessly. Poor thing, Tom hears Walburga Black's voice saying nastily. He's half-starved. Look on, Tom, they can't even take care of themselves.

The boy notices Tom's eyes on him and grimaces, a little, around a mouthful of white flesh.

Tom has known for years that he has a particular itch. It is a certain desire regarding men, but also women; not to slake his lusts in something warm and tight, as schoolboys do, but to hurt. It's a bit trickier to manage, with his wand slid in his sleeve rather than comfortably in reach, but several more times the fantasy spills into his conscious thoughts. The boy being hurt. And Tom Marvolo Riddle (I am Lord Voldemort) can do this so much better than a dirty peasant with a hunting-knife. So much better.

His fingertips ache with spells he cannot yet cast -- will he cast Crucio on the boy until he vomits and his odd dark eyes stream tears? Everbero, delight him with the purple flames even as it stuns him stupid. Or schoolboy tricks, little jinxes that were well enough fit to drive Muggles mad. Such fine plans! And the boy will call him his lord and master, and Tom will -- make himself rid of him. Kill him, one would suppose -- Obliviate him? Tom is in another country here, unsupervised, unaccompanied; the freedom thrills every particle of him.

The lofty part of Tom's nature is spurring him onward, to cease dallying by rail travel and find the diadem before another does, but what other is there? What challenger? He can hardly Apparate across Europe, and broom travel is conspicuous and dissatisfying. Consider it a Grand Tour. A brilliant wizard walking among the dirty and the diseased and the poor, charming the feeble-minded and hardly yet using his wand. Solitary slumming.
But his plans of finding other wizards -- in a countryside devastated twice, by the likes of Grindelwald as well as Muggle peasant upstarts -- are crumbling.

As Tom drifts out of the compartment, he comments in airy French that the boy might join him if he cares to. When Tom disembarks the train, the boy follows him.

"Looking for more apples?" Tom cannot resist teasing him a little, but the stranger stares at him levelly, in bright-eyed silence. (He doesn't carry himself like the other Poles, nor like a German.)

"Don't fret yourself. I knew you weren't a beggar. Won't you come with me?"