Warning: SPOILERS for the One Of Us Is Lying finale.
The Peacock Original series One of Us Is Lying is based on the book by Karen M. McManus but makes a major change to the reason behind Simon Kelleher's death. The result of an allergic reaction to peanut oil, Simon's (Mark McKenna) death happens in One of Us Is Lying episode 1, and once the police rule it a murder, his four classmates, Cooper (Chibuikem Uche), Bronwyn (Marianly Tejada), Addy (Annalisa Cochrane), and Nate (Cooper van Grootel) become suspects. One of Us Is Lying follows the four as they investigate their peers to try to get to the bottom of how and why Simon really died.
One of Us Is Lying uses stereotypes largely ironically to drive home its point about how trapped the characters are in their day-to-day lives and reputations. Even the supposed twists and secrets that accompany each character come as no shock: Addy, the pretty popular girl, cheated on her boyfriend; Bronwyn, the star student, cheated on a test to keep up her GPA; Cooper, the varsity athlete from Mississippi, is secretly gay; and Nate, the bad boy, led to a classmate's overdose by selling drugs. One of Us Is Lying's high school stereotypes are the basis of Simon's social critique, but the show makes one very significant change to his motivations from the book.
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In One of Us Is Lying season 1's finale episode, the group learns that Simon was actually the one who planted the peanut oil that killed him, intending to prank everyone else in detention by having a severe allergic reaction. But Simon's plan relied on someone running to the nurse for spare EpiPens and saving his life—he never intended to die. The reveal gets worse when it's discovered that Addy's ex-boyfriend and Simon's ex-best friend, Jake (Barrett Carnahan), was supposed to help Simon pull off the prank but instead hid the EpiPens to kill Simon and frame "Murder Club" (an homage to The Breakfast Club), specifically Addy, who cheated on him. However, this is a pretty big change to Simon's death in the book One of Us Is Lying.
One Of Us Is Lying Changes Simon's Death In The Book
One of Us Is Lying changes the book's version of Simon's death, primarily in terms of motive. While the method remains the same, in the book, Simon always planned his peanut oil prank to be a real suicide and merely asked Jake to help him carry the plan out. As an added bonus, Jake could plant evidence on Addy that made it look like a murder she had executed. Though One of Us Is Lying's book and show versions of Simon's prank and death are similar, Simon's death being an intentional act of suicide has a major impact on the show's ending and tone and changes his character significantly.
In One of Us Is Lying, Simon accuses his classmates of living in a John Hughes movie, looking down on those who play out high school stereotypes while proudly relishing his outcast status. Simon's friends actually encourage Murder Club to rule out suicide, knowing that Simon wouldn't do it. Removing the suicidal aspect of Simon's character makes him a very different figure in the show. While the book makes his death more tragic, the adaptation of One of Us Is Lying gives it a more sinister edge. While the book has plenty of twists and turns in the case of Simon's death, in the show, there is a real murderer on the loose who would gladly kill again, which helps set up One of Us Is Lying season 2.
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Because Jake is a murderer, not just a revenge-bent ex-boyfriend, the final episode, "One of Us Is Dead," has much higher stakes. In a scene straight out of a horror movie, Jake actually chases Addy through the woods with a loaded gun, and when the whole group arrives to save her, he's willing to point it at everyone. In the end, Jake is the one who gets shot and killed, which is another big One of Us Lying book change, in which he is alive and arrested in the end. Jake's death gives the One of Us Is Lying show a far darker and more unstable ending, and sets the series up for a potential season 2. By making such a big change to the book's version of the story behind Simon's death, One of Us Is Lying has indicated that it will likely deviate further if the show continues.