Admiral William Cornwallis gives Hornblower the distasteful task of arranging McCool's execution for desertion from the Royal Navy.
Cornwallis insists that McCool is to make no final speech before his execution, so that he cannot try to incite mutiny among the Irish sailors in Renown's crew.
The compartment is stuffed with currency notes and secret correspondence to other Irish rebels, in fact "Everything one would need to start a rebellion," as Hornblower comments to himself.
Hornblower, revolted at the spectacle of McCool's execution and suspecting the money could be French counterfeits, decides to spare other Irishmen from the gallows and throws the chest overboard.
Later, "when the Renown lay in the Hamoaze, completing for the West Indies," he discovers that McCool actually left no widow, and the chest was intended to reach an Irish revolutionary society.