Andrew is the most self-enclosed of the Costello brothers, even beyond Phillip’s occasional vacuity. He has great respect for his father – he is, after all, studying at the same College of Medicine that his father did.
On the other hand, whilst Dr. Costello is well involved in the war-effort and will not take his eyes away, Andrew takes a far more theoretical side to Medicine than his optician father does; Andrew studies for his intellect and his morality. And it is for this, too, that he sometimes chooses to fight.
So on whose side is he? Neither, in fact. Andrew acts as a barrier between the two sides. He will marry if he falls in love, but he doesn’t plan on falling in love, for his work means more to him; he will follow tradition merely to keep his father happy, but he does not go against tradition to strike his father, as Phillip and Peter seem to.
In this way, Andrew is the least eligible of the Costello bachelors, and the least observed by the papers. One wonders if he has friends inside press whom he asks to draw his name away. His opinion about the Costello name and any possible tarnishing of it is unclear. Andrew is deep within his thesis to argue with Rion or Phillip. Certainly, he would lose his house and books if the Costello fortune fell, but Andrew is likely to pick himself up and continue being a theoretical doctor in poverty.
Andrew portrays the ambiguity of those who are willing to change or willing to stay. He is a confirmed bachelor, but, unlike Rion, his sexuality is not unclear.