For a movie that has without a doubt the least tantalizing title for an action/thriller in recent memory, ‘The Accountant’ is far more entertaining than you’d expect. Unfortunately, it’s also the type of movie that promises more than it can deliver.

For a while, ‘The Accountant’ seems like a clever bit of pulp with some unique characters portrayed with unexpected gravitas by an overqualified cast and a handful of decent boom-boom fight scenes. It’s very much a B-movie, just one with more successful drama than most. Unfortunately, once the action revs up and this thing goes full genre, the human element gives way to the cartoon and things get so convoluted and downright silly that all good will vanishes. As far as mainstream star-driven action/thrillers go, you could do worse. But it’s unlikely that Ben Affleck or Warner Brothers will see this expand into the franchise that they seem to be setting up.

As you may have gathered from the marketing materials, Ben Affleck plays the accountant of the title. Christian Wolff (yes, that’s really the character name!) is an Autistic math whiz who may have trouble communicating with people, but sure know how to work them numbers. He’s hired by a robotics company run by John Lithgow (whose mere casting in any sort of mystery/thriller tends to feel like a spoiler) to check the books. A young accountant (Anna Kendrick, as almost inhumanly adorable as always) has spotted something fishy in the files. Wolff was hired to use his uncannily obsessive mind to sort it out. His skills do indeed deliver the goods, and as soon as he starts finding problems, a contract killer (Jon Bernthal) starts taking out members of the company. Meanwhile, J.K. Simmons plays a big dog in the Treasury Department who, along with his top agent (Cynthia Addai-Robbinson from ‘Arrow’), seek out a mysterious accountant with a possible professional killing streak. Hmmm… think these stories might be connected?

It’s all pretty silly potboiler stuff. While the tone is for the most part one of po-faced sincerity, director Gavin O’Connor and the cast are at least willing to acknowledge the absurdity of the extremes and pepper in some humor. Affleck might be limited as an actor, but he has movie star presence. In a role that demands he show as little emotion as possible, he doesn’t have an opportunity to go too far. He’s kind of charming as the monotone numbers man/killing machine who wishes he could reach out emotionally, and he shares some nice chemistry with Anna Kendrick (who’s stuck in a shallow potential love interest role that she somehow transforms into a lovably quirky/funny character through sheer force of will). Simmons and Bernthal also have no problem mixing dry humor and pained drama, lending credibility to cartoon characters in impressive fashion. This is an action movie populated by character actors, and they know exactly how to handle the heightened material, for the most part.

O’Connor (‘Pride and Glory’, ‘Warrior’) handles the plotting and world-building of his picture with ease, moving things along at a nice clip and mixing quirky comedy with brooding intensity. The setup is certainly unique and the tone makes everything feel a little off in a good way. Unfortunately, once the mysteries are solved and ‘The Accountant’ transforms into a conventional action movie, things get very generic very quickly. While the movie has some nice shootouts and the score/editing rise in a manner that suggests intensity and excitement, the story (particularly the backstory) also grows increasingly absurd. Meanwhile, the tone oddly gets more serious. Perhaps I missed some sly camp or parody, but by the end, ‘The Accountant’ starts getting the wrong kind of laughs. It’s a shame to watch the movie fly off the rails when it should be serving up a satisfying climax.

Weirdly, the flick almost feels like Affleck’s attempt to launch his own Jason Bourne-style action franchise for grown-ups. There’s nothing wrong with the ambition, but it’s strange that he’d want to create a second franchise while also locked in to playing Batman for a decade (both Warner Brothers productions, not coincidentally). That seems like an exhausting entanglement. For the sake of the star’s schedule, it’s probably good news for him that this one likely isn’t strong enough to sustain a sequel.

There’s an oddball action/comedy buried in ‘The Accountant’. Sadly, the whole thing falls apart right when it should be soaring into bullet-strewn popcorn nirvana. Even so, at least it’s never boring, which is the last thing most would expect when buying a ticket for a movie called ‘The Accountant’.