The Skulls

Lucas "Luke" McNamara (Joshua Jackson) is a working class former delinquent attending university and hoping to be recruited in to the elite secret society known as the Skulls so he can move on to Law School with their financial help. His friends are his roommate Will Beckord (Hill Harper), who is studying journalism and writes for the school paper and Chloe Whitfield (Leslie Bibb), a girl he hasn't admitted his true feelings for thinking her out of his league.Lucas get "tapped" to join the Skulls and during the initiation meets Caleb Mandrake (Paul Walker) and the two steal the weather vain mascot of the Snake & Skeleton society as part of their test. As part of the accepting ceremony, Lucas and Caleb become "Soul Mates", partners and bothers in the society. It is revealed that Caleb is the son of the current Skull head chairman Litten Mandrake (Craig T. Nelson). During a lavish party on the Skulls island Lucas befriends Senator Ames Levitt (William Petersen) who happens to be Mandrake's "soul mate", but there is tension between the two.Will, the roommate, is hurt that Lucas must now keep secrets from him and breaks into the Skulls chamber by stealing Caleb's key and rule book in order to write a story about the society. Caleb confronts Will there and as Will tries to escape he falls from a Dias and breaks his neck. The Society, directed by Mandrake, cover up Wills death to look like a suicide hanging but Lucas begins to suspect Caleb of murder when he finds Caleb's rule book among Will's things.Lucas recruits his old delinquent friends to help him infiltrate the society and find where the surveillance tapes from the night of Will died are being held. Caleb confronts Lucas back at his dorm room and warns Lucas not to go digging into what happened as the Skulls are always listening and watching, the rooms are bugged, and he is putting himself and even Chloe in danger. Caleb explains how it was an accident that Will fell down.Meanwhile, the Skulls Chairmen meet and Mandrake calls a vote to secretly remove Lucas from the society by forcefully admitting him into one of their mental hospitals. The vote is defeated by Senator Levitt who feels the society is taking measures too drastic, but he is blackmailed by Mandrake into passing the vote. Chloe and Lucas stage a public scene at school so the Skulls will think they are no longer acquainted and Chloe will be safe. Back in Chloe's room she admits to Lucas that she loves him.Lucas steals the surveillance tape from the Skull's archives and is chased down by Martin Lombard (Christopher MacDonald), a Skull member on the school's faculty and his goon. Lucas gets away with the help of Chloe and his friends and they review the tape, seeing that after Caleb left the scene at his father's direction and thinking Will dead, Will was actually still alive but he was then killed by Lombard by Mandrake's orders.Lucas brings the tape to Detective Sparrow (Steve Harris) who is in charge of Will's death's case. At that moment, Caleb is just leaving the police stating, having told the police that Lucas killed Will and covered it up. Upon reviewing the tape with authorities, it appears to be blank and Lucas suspects Detective Sparrow of switching the tapes and being under the control of the Skulls. Lucas is arrested and placed in a psychiatric hospital.Senator Levitt helps Chloe rescue Lucas, nearly comatose from medication, from the hospital. He leaves them to their own devices with the words "we live by the rules, we die by the rules". Chloe and Lucas are chased down by Lombard who is about to shoot Lucas when he himself is shot by Detective Sparrow who followed them from the hospital and is working for Senator Levitt.Lucas figures out that the Senator was telling him to use the Skulls rules to resolve the matter and heads to the Skulls island where the initiates are undergoing the last phase before being accepted as full members. Once there Lucas challenges Caleb to a duel, Mandrake tries to stop it but as Senator Levitt points out, he is bound to abide by the Skulls rules and they supersede all others.With pistols in hand, now loaded, Lucas attempts to reason with Caleb to admit to what happened to the congregated members and shake off his father's influence. Lucas drops down his gun and Caleb hesitates to shoot, spurring Mandrake to grab a pistol aiming at Lucas. Caleb shoots his father in the shoulder to stop him and as the members crowd around Mandrake, Caleb attempts to shoot himself but is stopped by Lucas.In the aftermath, Lucas is asked by Senator Levitt to assist him in leading the Skulls now that the Senator will become head Chairman. Lucas refuses "the honour", realizing he was used by the Senator and states he will risk the consequences of leaving the society behind him.Lucas leaves the island and meets back up with Chole, walking off together.

Question: Who challenges Caleb to a duel?
Answer: Lucas