<P> Waking up in Carter's bed again, Tree convinces Carter of her predicament by showing that she holds foreknowledge of the day's events . Tree admits to Carter she doesn't like who she's become; she has also grown distant from her father ever since her mother passed away three years ago and that they had shared the same birthday . Tree catches a local news report on John Tombs, a serial killer who is being held in the hospital on her campus . Concluding that Tombs is her killer, Tree rushes to the hospital to warn of his escape . Tombs breaks free and nearly kills Tree, but Carter follows and rescues her . Unfortunately, Tombs snaps Carter's neck before chasing Tree to a nearby bell tower where she manages to subdue him with a crowbar . Realizing that Carter will remain dead if she doesn't restart the loop, Tree hangs herself from the tower . </P> <P> During the next loop, Tree goes around righting the various wrongs she has caused, ending her affair with Dr. Butler, finally meeting with her dad to resolve her inner grief, and resolving to be a kinder person . That night, she prepares to stop Tombs . He manages to get the upper hand on her until Tree utilizes a campus - wide blackout that occurs during her loops to disarm him and shoot him to death . Relieved to finally be free, she celebrates her birthday in Carter's room and eats the cupcake given to her by Lori . </P> <P> However, the next morning Tree wakes up again on her birthday . Confused and distraught over the fact that killing Tombs didn't stop the time loops, Tree returns to her room in order to run away, where Lori offers the cupcake again . Tree realizes that she had died in her sleep, and also notes that this was the only time she had ever eaten the cupcake . Tree realizes Lori is the true killer; Lori had poisoned the cupcake, but when Tree didn't eat it, she utilized her job in the hospital to frame Tombs for Tree's murder . Lori confesses she was jealous that Dr. Butler had shown interest in Tree over her before the two fight . Tree manages to stuff the cupcake into Lori's mouth before kicking her out of a window, sending her falling to her death . </P> <P> Tree and Carter muse over the day's events back in the restaurant, and he offers her his room for the night, also commenting her situation is a lot like the film Groundhog Day . Tree wakes up the next day believing to be in another loop, but it turns out to be a prank by Carter and the two share a kiss . </P>

Who kills the main character in happy death day