River Marne, after a struggle that had lasted for two weeks.

In a battle following this decisive engagement--while returning from a
successful raid--Captain Harry Anderson, who had accompanied them, was
critically wounded and, together with Hal and Chester, taken prisoner.
Hal and Chester, with a French army dog they had rescued from the wrath
of a German officer, were taken almost immediately to Berlin.

There, while strolling about the street one day in company with the
German officer in whose charge they had been placed, they were made, to
their surprise, the bearer of an important communication to the Russian
commander-in-chief. It happened in this wise:

An English prisoner, recognizing them, made a dash for liberty and
succeeded in passing the document to Chester. The lad secreted it.
Finally, through their resourcefulness, the lads managed to make their
escape from the German capital and reached the Russian lines by means of
an airship.

Here they put the document into the hands of Grand Duke Nicholas, who, at
their request, assigned them to a regiment of Cossacks.

The lads immediately made a good friend of a huge Cossack, Alexis
Verhoff, a man of immense prowess and great strength, and with him saw a
world of fighting. In a battle with the enemy, Marquis, the dog who had
accompanied them, was killed. Later, while they were making their way
back to England by airship, Alexis, who accompanied them, was wounded on
the coast of Sweden, where their machine, crippled by the fire of German
aviators, had fallen.