He knew, he announced, that Prussia was their destination.
He had discovered it at the time of their capture from certain papers that he had found in a portmanteau of the Marquise's.

He discussed the matter with La Boulaye, and it was now that Caron had occasion to congratulate himself upon his wisdom in having elected to remain behind.
The Captain proposed to recall the fifty men that were watching the roads from France, and to spread them along the River Sambre, as far as Liege, to seek information of the way taken by the fugitives.

As soon as any one of the parties struck the trail it was to send word to the others, and start immediately in pursuit.
Now, had Charlot been permitted to spread such a net as this, the Marquise must inevitably fall into it, and Caron had pledged his word that she should have an open road to Prussia.

With a map spread upon the table he now expounded to the Captain how little necessity there was for so elaborate a scheme.

The nearest way to Prussia was by Charleroi, Dinant, and Rochefort, into Luxembourg, and--he contended--it was not only unlikely, but incredible, that the Marquise should choose any but the shortest road to carry her out of Belgium, seeing the dangers that must beset her until the frontiers of Luxembourg were passed.
"And so," argued La Boulaye, "why waste time in recalling your men?
Think of the captives you might miss by such an act! It were infinitely better advised to assume that the fugitives have taken the Charleroi-Dinant road, and to despatch, at once, say, half-a-dozen men in pursuit." Tardivet pondered the matter for some moments.
"Yom are right," he agreed at last.