Atonement starts off by introducing the reader to the main character, Briony Tallis who is a 13 year old ambitious and imaginative writer with dreams and visions of becoming famous one day. Briony has written and prepared a play for her older brother Leon, who is returning home from London, where he lives and works, for a weekend with his family. Three cousins from the north arrive, Lola, Jackson, and Pierrot, to spend the summer at the Tallis home while their parents (Hermione and Cecil Quincey) are supposedly attempting to work out their differences.
Briony giver mother a copy of the play she has written called "The Trials of Arabella." Her mother, Emily Tallis, likes the play when reading it, as does her sister Cecilia, although somewhat condescendingly. As soon as her cousins arrive, Briony begins to assign them roles and attempts to direct them in the upcoming performance that is to be put on for her brother the next evening (for a complete description of the play, see the bottom of page 4).
Lola, two years older than Briony, challenges the director/playwright (and manipulates her) for the lead part of Arabella in the play, which Briony finally secedes after coercing her three cousins to take part. Lola further mocks the lines in the play adding a distancing animosity between the two female cousins and the twins pay little to no attention to Briony's direction. Collectively, this destroys Briony’s vision of a spotlighted moment and perfect evening prepared for her brother’s return.
The play Briony sets out to direct and perform is noted as having a high point of satisfaction when her mother reads it, and everything else about it would be "dreams and frustrations." This is a obvious foreshadowing of the mood of self-retribution and theme of lost innocence to the book. Immediately, the notion of literary tradition is discussed, McEwan attaches fairytale and folk lore to childhood simplicity. Briony feels trapped in her younger body, comparing her older sister's enthusiasm to the play as more of condescension than sincerity.
The introduction to relationships and love in the book is also sour. We have Emily and Jack Tallis who never see each other, and Hermione and Cecil Quincey, who are going through a divorce, sending their children to be looked after by the Talis's. This an opportunity for McEwan to set the tale of bitter love in others, and then juxtaposing Cecilia and Robbie's love as being sublime and sweet.
The play Briony writes, "The Trials of Arabella" are a metaphor for what is about to come of Briony. The "spontaneous" (remember, all of Part One happens in a day) child is "inexperienced" and about to commit a crime that will see the world "rise up and tread on her."