On the drive into New York, Tom discovers that Myrtle is going to be moving away with her husband. Ironically, Tom seems to be losing both his wife and his mistress in the same afternoon. Also, the same thing is happening to both Tom and Wilson. They both have discovered that their wives are leading secret lives.
While this turn of events is happening, a series of ironic misunderstandings are also happening. Myrtle sees Jordan and assumes that she is Daisy. George sees Gatsby's car and assumes that it is Tom's.
As they were about to leave there was an incident between Tom and Gatsby. Gatsby asked if they would all use his car but Tom suggests that he take Gatsby’s car into town while Gatsby follows in Tom’s car. Gatsby tries to object by asking if Tom’s car has enough gas and Tom responds,
“Plenty of gas,” as he looked at the gauge. “And if it runs out I can stop at a drug-store. You can buy anything at a drug-store nowadays.”
It is quite ironic that Tom decides to drive in Gatsby’s car when he knows that there is something going on between his wife and Gatsby—yet he allows Gatsby to drive off with Daisy in his car.
The central irony of chapter seven is that while everyone is pretending to be having a “good time,” the hatred and hypocrisy that Tom, Gatsby, and Daisy share is actually finally boiling over. Their outing to the city in search of something to do is transformed into a open battle between Gatsby and Tom, ostensibly over Daisy. There are other little ironies as well. For example, Tom is constantly asserting his ownership of women, and having that ownership undercut. First, Daisy undercuts Tom’s authority when she tells Gatsby that “He always looks so cool,” a coded message of love that Tom finally understands, causing him to demand they all go to town, a way for him to reassert control and dominance over the situation, just as his decision to drive Gatsby’s car is a way for him to take “control” of Gatsby’s things. Second, it is this decision that forces Tom to stop at Wilson’s garage for gas, where he learns Wilson is planning to take his wife, Tom’s mistress, away with him to California.
As Fitzgerald writes, “There is no confusion like the confusion of a simple mind, and as we drove away Tom was feeling the hot whips of panic. His wife and his mistress, until an hour ago secure and inviolate, were slipping precipitately from his control.” Tom is desperate to regain control of the situation, so he directly confronts Gatsby at the hotel, a scene that causes Gatsby and Daisy to leave, and eventually results in Daisy running over Myrtle in a horrible accident. Tom and Gatsby's battle over Daisy is ironic because she does not appear to be worth fighting for (she seems incapable of committing to either man) and the shared life Tom alludes to in his fight (“Daisy and I have shared things you’ll never know”) seems every bit as empty as the fictionalized life Gatsby has created for himself. In other words, Tom and Gatsby's fight is ironic not because the stakes are so high, but because nothing is really at stake at all.
The final ironic twist, of course, is that Daisy is the one responsible for Myrtle’s death. Without knowing it, Daisy accidentally killed her husband's mistress. Gatsby’s decision to cover up her involvement leads directly to his death at the hands of Wilson, who (again, ironically) has confused Gatsby with Tom, two men who seem to be very different but who end up being very much the same.