This is the story of the investigation of a drug overdose by a college senior, played by Mia Kirshner. Did her "friends" from an exclusive rich girl sorority have anything to do with her untimely OD? Unfortunately, Alicia can't help explain things because she's in a near-death coma for the entire movie, so the story is told in flashback.
Kirshner's character came from the wrong side of the tracks, so she would ordinarily have no business associating with the well-to-do sorority girls played by Meredith Monroe, Dominique Swain and Rachel True (looking much like the "Clueless" trio updated to college age). But a chance sociology assignment throws her in with the rich set, and the less fortunate girl spends much of her time fretting about financial aid to pay for law school.
The cause of drug overdose is the central mystery. Was Kirshner's character not the "innocent, goody-goody" poor girl that she was made out to be, and did she bring this fate upon herself? Or did the rich girls have it out for this supposed "friend" but rapid rival (for both boys' and girls' attention), and did they push her into the dangerous situation? The audience may come to feel that it is a combination of both factors that led to accident -- or was it a crime?
I know that this movie is not being well-received by critics, but I think that's because the reviewers are taking it much too seriously. (The movie takes itself a little seriously as well, but that doesn't mean that you have to.) Think "Wild Things" with less intentional humor -- the laughs in "New Best Friend" do not seem to be intended by the director/writer. I would especially recommend it for boys or girls under 17 -- sneak into the theater if you have to; it could become a cult classic by the time you reach college....