He must confine himself to listening.
The first words exchanged were of no importance--to him at least--but they allowed him to recognize the voices of the man and woman whom he had heard at Nijni-Novgorod.

This, of course, made him redouble his attention.

It was, indeed, not at all impossible that these same Tsiganes, now banished, should be on board the Caucasus.
And it was well for him that he listened, for he distinctly heard this question and answer made in the Tartar idiom: "It is said that a courier has set out from Moscow for Irkutsk." "It is so said, Sangarre; but either this courier will arrive too late, or he will not arrive at all." Michael Strogoff started involuntarily at this reply, which concerned him so directly.

He tried to see if the man and woman who had just spoken were really those whom he suspected, but he could not succeed.
In a few moments Michael Strogoff had regained the stern of the vessel without having been perceived, and, taking a seat by himself, he buried his face in his hands.

It might have been supposed that he was asleep.
He was not asleep, however, and did not even think of sleeping.