At this point, the Doctor reenters the narrative. He reasons that the solution to this problem may be splitting up Tom and East rather than expelling them. Discussing the situation with their schoolmaster, he decides that it would steady Tom to have a younger boy put in his charge. This is when we meet George Arthur, the young son of a clergyman. He is quiet, painfully shy, and is assigned to share a study with Tom. Tom is a bit miffed, since he'd been planning on sharing the study with East. He's somewhat mollified by the fact that Arthur seems a good sort, and has a lot of nice things with which to outfit their room.
Tom finds himself at a loss as to what to do with Arthur. Used to the rough and tumble, boisterous life of the Schoolhouse, he is unsure how to deal with a boy who barely talks, or worse, meekly agrees with everything he says. Tom finds this extremely frustrating, but feels responsible for Arthur, and fears that other boys will make his life miserable. He tries to bring Arthur out of his shell, and advises him on how to conduct himself to avoid ridicule:
"...you must answer straight up when the fellows speak to you;
and don't be afraid. If you're afraid, you'll get bullied. And don't
you say you can sing; and don't you ever talk about home, or your
mother or sisters."
This episode marks the beginning of a transformation in Tom's character as, influenced by Arthur's friendship, he begins to mature and change- or at least question- many of his opinions and behaviors.
Arthur's influence over Tom- and thereby, East- is just as marked, though gradual, so that they don't even realize how much they're changing. This transformation is demonstrated through various incidents, such as Tom's moral conflict over the use of Latin cheat sheets, and East's crisis over his confirmation.
T.B.S.D. covers a number of years, leading up to Tom's graduation. The last chapter skips several years ahead, detailing Tom's return to Rugby after the death of the Doctor, and his reflections on how his early education shaped the man he has become.