Act I starts at the very beginning (a very good place to start) and ends when Lucy witnesses the murder – it changes her perspective on life, the universe, and everything, permanently.
Lucy’s rejection of George in Chapter Sixteen (“Lying to George”) marks the end of Act II – we’re not sure if she can repair the horrific muddle she’s made of her relationships, and if she will ever come to terms with her true feelings for the young Mr. Emerson.
At the last minute (Chapter Nineteen), old Mr. Emerson makes Lucy realize just how confused and untrue to herself she’s been. Things between the young lovers are resolved just in the nick of time.