<P> Henry sees Christina being abused by her stepfather, Glenn, the local police commissioner . Henry reports the abuse to social services and the school principal, Janice Wilder, but Glenn has connections throughout the local government, and Wilder is reluctant to challenge the commissioner without "conclusive evidence". Henry is unable to get the authorities to launch a serious investigation that would protect Christina . Henry tells his mother that when someone is in trouble, those who can help must take action . He develops a detailed plan to rescue Christina that he memorializes in a notebook . After a violent seizure, Henry is taken to the hospital, where he is diagnosed with a brain tumor and undergoes surgery . Anticipating his death, he tells Peter to give Susan the notebook . Days later, Henry dies in Susan's arms in the hospital . </P> <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 Henry's 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>

Does she kill glenn in the book of henry