Alternative Character Interpretation: Ellie and Mr. Morton debate if Marco is being controlled by the "dark forces" or is a troubled child unable to handle an unstable home situation. Mr. Morton, who survived an attack from Marco, thinks he's being manipulated to murder Will and fulfill his destiny. Ellie posits that Marco is a teen who is responsible for his own actions but still feels sorry for him. Will seems to agree with Ellie, telling Marco in the climax that just because their parents are messed up doesn't mean that the two brothers have to be.
Anvilicious: The ending of the book hammers home that Parental Favoritism hurts both the favorite child and The Unfavorite. Will's dad is a stern general that wants Will to follow in his footsteps and go to military school, without even considering if that's even what's best for Will. Not to mention that after Marco gets arrested for nearly shooting Will, his response isn't relief that Will was unhurt or guilt about the fact that he motivated Marco to want to shoot his half-brother, but kicking out his favorite child for refusing to go to military school Notable that Ellie's parents tell him, when Will shows up at their doorstep with his dog and clothes, is he can stay for as long as he likes and not have to talk to his dad.
Cry for the Devil: Marco's Villainous Breakdown and Motive Rant at the climax of the novel, while holding Ellie and Will at gunpoint. He talks about how for all his life, he was under the thumb of a stepfather that never appreciated him, and always compared him to Will, who was the golden child. Said man also got his real father killed, and fathered Will out of wedlock. So they're related, and Marco loses his mother all over again as well as the reality of the situation. Will and Ellie even agree that Marco was unfairly treated, with Ellie telling Marco to kill their father for his assholery but Will is an innocent party. Mr. Morton hopes that a stint in jail plus being cut off from the dark forces will help Marco come around.
Viewers Are Geniuses: While the book explains a lot about Arthurian legend other details aren't really explained and its just expected that the readers know it. For example, when Ellie is revealed to be the Lady of the Lake, there is almost no explanation as to who that is.
YMMV for the movie
Broken Base: The movie is more inspired from the book than based on it. Any fan of the book couldn't enjoy the movie completely without a WTH moment, but many people who grew up on the film appreciate it for what it is.
In The Movie, they changed Ellie to Allie. Because Allie is more like Arthur- a (not-very) subtle clue of who she is!
Also Will and Lance both being Arther's Knights (as well as Marco). Will's shield bears a golden Lion, the standard of Gawain.
Fridge Logic: Allie's mother recites a stanza from The Lady of Shalott to Will when she meets him for the first time. Two problems; the stanza describes Lancelot, not Arthur as we're supposed to think Will is, and she describes the poem as 'how Arthur became the leader Camelot needed'. Arthur's not even in the poem!
