How does the author use foreshadowing in Mr. Midshipman Hornblower?

In the chapter, Hornblower and the Examination for Lieutenant, the fire ship's original crew captures Hornblower—his second stint as a prisoner of war. He is almost immediately rescued, however, and then a brief but sharp exchange between two captains ensues and ends in the promise of a duel. Hornblower finds this inexplicable and yet only a few years earlier he himself had found exhilaration and intense meaning in his own challenge and duel. The recurring echo illustrates how far Hornblower has developed as a young man. Now twice a prisoner of war, Hornblower's ultimate fate in the novel is foreshadowed heavily. His obvious concern for imprisoned men will, as these things go in heroic fiction, ensure that he will be well treated when his turn comes around.