Final answer:
The sentence "Yes," said Easton, "I must go on to Leavenworth," contributes to the story's irony by subtly hinting at Easton's true identity, potentially revealing that he is a convicted criminal and creating a contrast with any preconceived notions about his character.
Step-by-step explanation:
The sentence "Yes," said Easton, "I must go on to Leavenworth," plays a significant role in the establishment of the story's ironic tone. Without having the context of the entire story, one might interpret this statement in several ways - perhaps Easton is going back home, or he has business there, etc. However, assuming that Leavenworth is the location of the penitentiary, one can deduce that this sentence likely contributes to the story's irony by hinting at Easton's true identity, potentially as a convicted criminal, which is not yet known to Miss Fairchild or is contrary to what she believes. This contrasts sharply with any preconceived notions the reader or Miss Fairchild might have about Easton, thus highlighting the irony in his straightforward admission that carries significant hidden weight.