Arthur is 10 years old and has maintained a writing journal since he was seven. He knows his mum is going to have a baby, but he's not been told. Instead he is shipped off for the summer to stay with Great-Aunt Elda and Great-Uncle Wrisby. They have a most unusual pet chicken called Pauline who only answers to the French language. Arthur is fascinated by his new abode. "The house was a book, and Uncle Wrisby and Aunt Elda the characters." He's asked to make a list of what he doesn't like to eat, and he's given a wonderful room at the top of the house -- a room with a view -- as well as a pair of binoculars (Uncle Wrisby's equivalent of Arthur's journal writing). How you can look through either end particularly fascinates him. Aunt Elda shows him the mockingbird -- and recites Randall Jarrell's poem about the mockingbird, which explores what is real and what is not.

Arthur feels excitement for the very first time. He learns to look at life close up and to consider whether it's more important to do or to say/write in life. Moira, a young girl neighbor who reminds him of a starling, is a do-er. She calls him Mouse -- until the very end of the book, when he proves his capability by delivering the piglets of Wrisby's pig Bernadette. Then she calls him Arthur for the very first time.

Arthur also learns to look at his parents in a new way -- and after avoiding reading their letters, he opens them.