The book begins as McCourt lands at Albany, New York, and quickly makes his way to New York City. Friendless and clueless about American customs, he struggles to integrate himself into American blue-collar society. He is then drafted into the US Army, sent to Europe, and rises to the rank of corporal. On his stay in Germany, he has confrontations with many people who try to show Frank how to get a Russian refugee girl to have sexual intercourse with him by giving her coffee or cigarettes. He is granted leave from the army as compensation for his exceptional service as a clerk-typist and goes back home to Ireland to see his family. He then decides to return to the US, where he attends New York University – despite never having graduated from high school. He falls in love with and eventually marries a middle-class American-born girl, Alberta Small (nicknamed Mike), whom he meets at university.
After graduating from NYU, he teaches English and social studies at McKee Vocational and Technical High School on Staten Island. There, he is forced to deal with apathetic, indifferent students. Eventually, he moves on to teaching at the prestigious Stuyvesant High School. At Stuyvesant, he revises his teaching style to end his reliance on books and other teaching resources, to become an effective teacher.
'Tis examines Frank's relationship to his family and his wife during this time (all his siblings and his mother move to America over the course of the book). Eventually, Frank's relationship with his wife turns sour, and they stay together as long as they do only because of their daughter, Margaret Ann (named after Frank’s sister who died in infancy, and his grandmother, who is described in Angela's Ashes). Nonetheless, Frank finally leaves them, an action he compares to that of his father leaving his family.
Frank's mother, Angela McCourt, is in increasingly bad health due to emphysema and dies in New York around the same time as Frank's father, Malachy McCourt, Sr., dies in Ireland. Frank goes to Ireland to bury his father and scatter his mother's ashes. The book ends after Frank and his brothers scatter Angela's ashes over the graves of her family.
"'Tis" was the final and only word of the last chapter of Angela's Ashes, while 'Tis ends with the spreading of Angela McCourt's ashes in Ireland. Frank McCourt has remarked in several interviews (perhaps joking) that he originally intended for each book to have the other's title.
Frank McCourt followed this book with another memoir, Teacher Man.
Frank McCourt: The narrator and author of the book and an immigrant from Ireland, he has a deep love for literature and eventually goes on to marry Alberta after attending NYU. He taught as a school teacher for the latter part of his life, despite many offers to work for higher pay in the auto industry and loading docks.
Alberta Smalls: Also known as "Mike" during her college years, she and Frank meet in college during one of their classes together. Although she had trouble dealing with Frank's frequent drinking problem, they push through together and eventually get married.
Tom Clifford: A roommate of Frank's before he left for high school, Tom eventually leaves for Detroit to work in an auto factory, and urges Frank to join him. Frank declines, citing his desire to go to college as reason to stay.
Margaret Ann: Named after Frank's sister, Margaret is born with birthmarks on her feet which Frank initially feels sullies her and ruins his perfect picture of his daughter running shoeless on the beach. He blames the black nurse for this, as well as his daughter's flat temples, which she acquired from pulling too hard to get the baby out. He quickly forgets about all this though, as his wife sobers up from the pain medication and is relieved to see her new daughter.
The title of the novel comes from the last sentence of the previous memoir, "Tis", an answer to a rhetorical question.
The memoir has been criticized because it ignores McCourt's marriage to psychotherapist Cheryl Floyd.
L.S. Keep of Entertainment Weekly, described the novel as a good successor of Angela's Ashes, concluding that "this book has the same clairvoyant eye for quirks of class, character, and fate, and also a distinct picaresque quality. It’s a quest for an America of wholesome Hollywood happiness that doesn’t exist, and it’s about the real America — rendered with comic affection — that McCourt discovers along the way. " Similarly, Margo Hammond of the St. Petersburg Times found the novel a good read, though McCourt was unable to provide a satisfactory narrative arch to the work. Commenting for the public radio station WKMS, Jacque Day called the novel "an exercise in humanity by a man with a rare gift for a story, and a brogue that sings on."