Enredo

At Oxford University, a professor and a grad student work together to try to stop a potential series of murders seemingly linked by mathematical symbols.

Martin (Elijah Wood), a PhD student in mathematics, enrolls at Oxford in the hope of meeting his mentor, Professor Arthur Seldom (Sir John Hurt). The young man manages to find lodging at Mrs. Eagleton's (Anna Massey's), but in this house, a stifling atmosphere prevails due to the landlady's attitude. Indeed Mrs. Eagleton, who happens to be a friend of Seldom's, is a haughty and unsympathetic woman who also stifles her daughter Beth (Julie Cox). At the university, things do not fare much better as Martin is put in his place by his idol during one of Seldom's lectures. But his private life changes for the best as he starts an affair with Lorna (Leonor Watling), a beautiful girl he met during a game of squash. One night, Seldom and Martin, who find themselves at Mrs. Eagleton's, discover her dead body. They are interrogated by the Police. Soon afterwards, they decide to lead their own private investigation.—Guy Bellinger

Martin (Elijah Wood), an American student at the University of Oxford, wants Arthur Seldom (Hurt) as his thesis supervisor. He takes accommodation in Oxford at the house of Mrs. Eagleton (Anna Massey), an old friend of Seldom. Also in the house is her daughter, Beth (Julie Cox), who is her full-time caregiver - which she resents bitterly - and a musician by occupation. Beth tells Martin that Seldom likes young girls. She also says that Mrs. Eagleton's husband and Seldom were good friends & developed theories together.

In a public lecture, Seldom quotes Wittgenstein's Tractatus to deny the possibility of absolute truth. Hoping to impress his idol, Martin disputes this, asserting his faith in the absolute truth of mathematics: "I believe in the number pi." Seldom humiliates him, ridiculing his arguments and making him look foolish in front of the audience.

Disillusioned, Martin decides to abandon his studies. There, he encounters his office-mate, a bitter mathematician Podorov (Burn Gorman), who also failed to become a student of Seldom's. Martin then returns to his residence, where he finds Seldom arriving to visit Mrs. Eagleton. The two men enter the house together and find Martin's landlady murdered. Seldom tells the police that he had received a note, after the conference with Mrs Eagleton's address & just saying "the first of a series". As Seldom is an authority on logical series, he argues that a serial killer is using murder as a way to challenge his intelligence. According to Seldom, "The only perfect crime that exists is not the one that remains unsolved, but the one which is solved with the wrong culprit."

Martin and Seldom discuss how easily the murder of the old lady might have been overlooked, particularly as she already suffered from terminal cancer, and Martin suggests that the murderer is committing 'imperceptible murders' - meaning that the killer is choosing victims who are already dying therefore meaning that the police would be less likely to suspect foul play. Beth admits to Martin that she was waiting for her mother to die so that she could have a life of her own, as she was going to die one day anyway.

Martin, Seldom and Lorna (Leonor Watling), a Spanish nurse with whom Martin has struck up a relationship, try to solve the mathematical clues as the murders continue. They have to contend with police suspicion, a rising body count and tensions among the three of them. There is a wide range of suspects, from the three principal characters to the mathematician Podorov and the old lady's daughter Beth.

Podorov tells Martin that 30 years ago Seldom's wife & Eagleton's husband were killed in a car crash when Seldom was driving. Seldom visits a patient at the hospital where Lorna is a nurse. The patient is one of Seldom's students who found a similarity between the logical thought patterns of extremely gifted and the ones who had been lobotomized. The patient, Carmen was also a cancer patient, & to explain this paradox, he performed a lobotomy on himself with a nail gun & had been rotting away in the hospital ever since. Seldom visits him as he had promised he collect his messages from "the other side". The patient writes 4 letters, the name of a woman.

The second murder happens & its the roommate of Carmen & was also a cancer patient. Another symbol is left as a clue in a series, but the solution is elusive. Beth becomes obsessed with Marin & is hurt when she finds he is having sex with Lorna. Seldom tells Martin that he used to have sex with Lorna a while ago & when they separated, she was angry. That makes her a suspect. Beth tells Martin she spoke to the police & told them that he was a homo & was obsessed with Seldom. The police get a psycho analysis of the note & conclude that the writer is a repressed homo & is trying hard to gain admiration, possibly of Seldom. This makes Martin a suspect. Beth is performing at a concert which Seldom & Martin attend. The conductor of the concert dies in front of everyone at the end & police recover the 3rd symbol.

Martin is having sex with Lorna & then the puzzle solves for him when he realizes that the symbols are part of a sect that used to perform medical surgeries using mentally retarded people as Guinea pigs. Martin remembers seeing a man in Lorna's hospital whose daughter was waiting for an organ donor, with the medical surgery book with those 4 symbols. That man is shown to be driving a bus full of mentally retarded people. Martin contacts the police who manage to stop a bus, but its the wrong one & has Seldom in it. The suspect bus drives by minutes later & explodes in a huge ball of fire. The dead man becomes the officially serial killer with the theory that he killed all the other people to create a serial killer alibi & his plan was to jump out of the bus before it exploded, but he failed. The bus was carrying many children who could have been an organ donor for his daughter.

Later Martin has an epiphany & tracks Seldom down. He alleges that there was no serial killer. Beth killed her mother to get her life back & contacted Seldom. Seldom wanted to help her as he felt responsible for the death of her father. So Seldom invented the whole myth of the serial killer & imperceptible murders to take the blame away from Beth. Only the bus driver jumped on this serial killer bandwagon to save the life of his daughter but ends up dying himself. Seldom agrees with Martin, but says Martin is the real culprit as Beth was in love with him & Martin inspired her to have a life of her own.