Mothballs: Iron Path to the Black Forest

Aksel Laurisden had heard many tales about exotic travellers in faraway lands and, despite being reasonably clever, he'd always believed they could be true. Since they'd sold their every belonging to fund their pursuit of the Obscured Man, he'd discovered the ugly truth. They weren't.

Verity, his little sister, had been struggling to sleep. As Septimus, his older brother, had reminded him during those rare seconds of rest bite whilst Verity found the path to dreamland, she had always been closest to Sebastian, their pet cow.
The bouncing of the carriage on the rails of pure iron had managed to lull Verity asleep, and she lay under a rough blanket on the cold metal floor, her chest rising and falling with dainty movements. Aksel and Septimus had taken blocks of coal from the mound in the corner of the carriage they were stowed away in and used them to sketch images, from the hastily packed blue prints that Septimus had stuffed his bag with, onto the white panelled walls of the carriage. "Are you sure you heard nothing?" Aksel said.
"I'm sure. Why they're so interested in the speech collar I've no idea." Septimus replied. He smiled at the brilliantly redrawn blueprint, before turning his attention to a selection of maps he'd pinned to the floor. "According to our research, the Obscured Man took a hidden route to Germany, intending to board the train on the other side of the Canal d'Alsace. Our train stops just before the bridge in about an hour and by midnight we'll be over the bridge and pulling to a halt outside the train station. The train then stops and doesn't start till midday. Furthermore, the Obscured Man is expected to get off at the station after. The distance between is a days travel meaning we have a day to track him down and make him tell us where Sebastian is."
There was a scream behind them and they spun to see Verity waking up. Aksel rushed over and knelt down. "Are you ok?"
"Yeah, I've just had that nightmare again." She wiped a veil of sweat from her forehead and climbed up. "What's the plan then?"
Septimus repeated what he'd just said and then explained the plan itself. "When we stop just before the bridge, we jump off the train, leg it up the side and climb aboard at the back of first class. The Obscured Man is meant to be quite wealthy, so that's where will find him."
"What if the train sets off without us?" Asked Verity.
"I doubt it, and I'm sure we could find someway to get back on." Septimus replied, but he was as early as confident as he sounded.

An hour passed but there was no sign of slowing down. Septimus flipped open his fathers pocket watch to reassure himself. There was a skeleton key tightened to the chain, a faithful reminder that Time is the Key, and his finger graced against it as he moved up to straighten his hat. There was a box leading from one corner of the room to the other along the joust. Inside were several taunt wires. The taunt wires vibrated with messages, resent at checkpoints dotted along every three carriages. Septimus had spent the first two days they'd been on the train designing and building a device to read the wires and he applied it to them as a new message rattled through. "They're not stopping."
"What!" Aksel cried. "Why?"
Septimus retuned his gadget. "An anonymous passenger requested for them to hurry to the bridge."
"The Obscured Man." Aksel realised.
"But we won't be able to get to the front unless we do it now." Verity said.
Septimus estimated the odds in his head. "Aksel, did you bring the goggles?"
"Yes, why?" Aksel replied.
"We're going to need something to keep the smoke from our eyes."
"Why?" Demanded Verity. "Why would there be smoke in our eyes?"
"Because we're going over the top. We need to run across the top of the train."