<P> Susan is distraught at Henry's death and has difficulty functioning, but when Peter gives her the notebook, she focuses on Henry's plan . Susan tries, but fails, to interest a nearby social services agency in opening an investigation . One night, from the window in Peter's bedroom, she sees Glenn in Christina's room and decides to carry out the plan . The notebook and an accompanying cassette tape describe a step - by - step plan to kill Glenn with a sniper rifle while covering Susan's tracks so that it will be impossible to trace the murder back to her . Susan's alibi is to be provided by executing the murder while both Christina and Peter are performing at a school talent show . </P> <P> Susan slips away from the talent show and puts the plan into motion . As she is about to pull the trigger, however, she realizes that Henry's plan, though ingenious, is the construct of a child, and that she must act as an adult . She immediately confronts Glenn and tells him that she is going to expose him for what he has done to Christina . Glenn replies that everyone will believe him, not her, and he tells her that he is going to call his police chief to come and bring her in . At the same time, affected by Christina's dance performance at the talent show, Principal Wilder decides to follow through on the abuse accusation and contacts the authorities . Glenn returns home, calls his relative at Social Services, and learns that an investigation is being opened into his abuse of Christina . As the police arrive at his house, Glenn kills himself . Susan legally adopts Christina as her daughter . She also finishes writing one of her children's books, as Henry had urged her to do . </P> <Ul> <Li> Naomi Watts as Susan Carpenter, the mother of Henry and Peter </Li> <Li> Jaeden Lieberher as Henry Carpenter, the title character and Susan's older son . </Li> <Li> Jacob Tremblay as Peter Carpenter, Henry's brother and Susan's younger son </Li> <Li> Sarah Silverman as Sheila, a waitress and Susan's best friend </Li> <Li> Dean Norris as Glenn Sickleman, the police commissioner and Christina's abusive stepfather </Li> <Li> Lee Pace as David Daniels, a neurosurgeon who operates on Henry </Li> <Li> Maddie Ziegler as Christina Sickleman, Glenn's stepdaughter </Li> <Li> Tonya Pinkins as Janice Wilder, the school principal </Li> <Li> Bobby Moynihan as John, Susan's and Sheila's boss at the diner </Li> <Li> Geraldine Hughes as Mrs. Evans, Henry's and Christina's teacher </Li> <Li> Jackson Nicoll as Morris, a boy who bullies Peter </Li> </Ul> <Li> Naomi Watts as Susan Carpenter, the mother of Henry and Peter </Li>

Who played peter in the book of henry