Some movies have unfaithful endings—the kind that don’t follow from their characters’ motivations, prior events or clues, and couldn’t possibly have been predicted by viewers at any point in the storyline. Imagine if “Twelve Angry Men” had ended with the one obstinate juror pulling out an M-16 and mowing down his uncooperative colleagues. “The Good Guy” is kind of like that, except it’s not just the ending.

This is the sort of movie where it almost feels as though the person who wrote the second page never read the first. A film where a character can tell a girl that he likes “Pride and Prejudice” because it reminds him of the hazards of first impressions, and then in the next scene be found rereading the book, explaining “I just met a girl who reminds me of Elizabeth Bennett.” Is he not listening to his own dialogue? The movie often gives that impression.

Worse still, rookie writer/director Julio DePietro doesn’t seem to realize that if you have to give your characters frontal lobotomies periodically to make your plot work and get your message across, there’s probably something fundamentally wrong with the script. The problem is that when a filmmaker both writes and directs, there’s no one there to point this out.

Saddled with the impossible task of portraying these discontinuous characters are a trio of television actors who apparently had slim pickings when it came to selecting their launch vehicle to the silver screen. Scott Porter (“Friday Night Lights”) plays the dashing Tommy Fielding, who looks to the audience like a high school senior doing his internship at a Wall Street firm, but whom the film helpfully tells us is actually a stock broker there. Painted from the start as “the good guy” in a depraved world full of cut-throats and egotists, Fielding is dating the lovely Beth Vest (Alexis Bledel of “Gilmore Girls” and “Sisterhood of the Traveling Pants”). Bryan Greenberg (“One Tree Hill”) is Daniel Seaver, the nerdy yet hunky computer guy at the brokerage firm whom Tommy gives a shot at a real finance job.

What follows is a predictable love triangle in which Fielding’s protégé slowly grows closer with Fielding’s girlfriend. But to move us along without waiting for such inconveniences as “character development,” the script decides to just drastically rewrite the personalities of the main cast on the fly.

Hence, there is Dan’s miraculous transformation from a borderline autistic into a Wall Street whiz who is also the life of Beth’s book club. (It’s a girls-only book club, but this film is far too clever to be derailed by such trivialities as believability.) Similarly, Beth trades men like Daniel trades personalities. It seems Tommy’s job keeps him too busy to hang out every single second of their screen-time, and so naturally she gravitates towards the only other male character in the story. Oh, and in case it’s not abundantly obvious, all-American Tommy is not what he seems either. At one point, in a particularly egregious move, the film even has him lie to the audience in narration, just so they don’t catch on. Really.

Almost as frustrating as this cardboard characterization is the fact that scattered throughout this rather awful movie are the makings of a very good one.  Director DiPietro is just in the wrong genre. Whenever the film strays into the territory of romantic comedy, it actually works. The lines are funny, the soundtrack is snappy, and the atmosphere is ideal. The actors are winning, if cookie-cutter, and know how to tell a joke. DiPietro is also a very artful showman, able to convey his characters’ emotions through unlikely angles and lush camera work. When his characters change—however absurdly—so does the film’s landscape. Unfortunately, DiPietro decided to try and teach his audience members a life lesson instead of just making them laugh.

“The Good Guy” is, in a word, contrived. The people in it are props, with actions dictated by the director just as much as anything else on screen. In this way, the film manipulates its characters, its plot, and its audience to teach a pseudo-sophisticated moral about how being true to one’s self is a greater pleasure than all the money, luxury, and girls that charm can buy. “The Good Guy” forgets that it’s hard for a film to preach integrity when its script has none.

—Staff writer Yair Rosenberg can be reached at yrosenb@fas.harvard.edu.