A slow-burn action-thriller that often feels as if it is trying to be the next "The Bourne Identity," "The Accountant" replaces amnesia with a developmental disorder and taut, fine-tuned storytelling with a lumbering, convoluted plot of dopey foregone conclusions. As was the case with his 2011 directorial effort "Warrior," Gavin O'Connor too often loses his way in forced showdowns and overwrought dramatics. His and screenwriter Bill Dubuque's (2014's "The Judge") self-indulgences are particularly a shame because when the exceptionally acted "The Accountant" works, glimmers of a far superior film shine through.

Christian Wolff (Ben Affleck) is a savant mathematician with high-functioning autism and, as Liam Neeson might say in the "Taken" franchise, a very particular set of skills. When his freelance accounting business is hired to examine the financial ledgers of Lamar Black's (John Lithgow) high-tech Living Robotics corporation, his discovery of illegal transactions places him and resident analyst Dana Cummings (Anna Kendrick) in immediate harm's way. Meanwhile, Treasury Department director Ray King (J.K. Simmons) and new assistant Marybeth Medina (Cynthia Addai-Robinson) move closer to uncovering Christian's identity and modus operandi.

"The Accountant" is at its best when it is focused on Christian and his unique way of demonstrating the warm feelings he comes to have for Dana. Hyper-intelligent but lacking in communication skills, Christian has been let down all his life—his mother walked out on the family when he was still a child—and expressing his emotions doesn't come easy. When Dana takes a friendly interest in him, then becomes the latest target of a shady hit job, he makes it his mission to protect her. Just as they are getting closer, though, the narrative takes a turn, breaking up these two compelling characters and leaving Dana absent for much of the film's second half. What replaces it is altogether less assured, leading toward gawky scenes of exposition and a key revelation in the finale that has been obvious from the very second hired killer Braxton (Jon Bernthal) comes into frame. This third act is especially problematic, growing saccharine and tonally awkward as interpersonal feelings are wrestled with and bonded over amidst a floor of dead bodies.

Ben Affleck (2016's "Batman v Superman: Dawn of Justice") is sympathetic and touchingly reserved as Christian Wolff, a man whose autism poses special challenges but whose disorder does not define him. A whiz at numbers and sharp-shooting, he shields a secret life that makes him a formidable opponent against those who want him dead. Affleck works particularly well opposite the always luminous Anna Kendrick (2015's "The Last Five Years"), as Dana, who holds the viewer at rapt attention and interest for every moment she's in view. Kendrick is wholly believable as a shrewd, down-to-earth accountant who has chosen what she presumes is the safer career path over her real passion for art. Affleck and Kendrick have delicious chemistry, no more so than during a moment of connection where Dana begins to break through to Christian while hiding out in a hotel suite.

"The Accountant" ends on a lovely, low-key note that stands at direct odds with the overcooked climax preceding it. The film is consistently uneven like this, graceful, winning and even tense moments sharing time with frequently slack pacing and director Gavin O'Connor's tendency toward a heavy hand. The picture exhibits more intrigue than one might expect from a movie sleepily titled "The Accountant," but there are also enough lulls for one to wish the script had been reimagined. Giving main attractions Ben Affleck and Anna Kendrick an uptick in screentime together would have been a great start—with or without the threat of flying bullets.