Even though I was seated comfortably in a mostly empty theater for a late-night showing of Black Mass, there was little the silver screen could do to keep James Bulger’s steely blue eyes from piercing me straight to my core. The Boston crime drama, directed by Scott Cooper, puts its eggs in two baskets, using James “Whitey” Bulger (Johnny Depp), the infamous kingpin of the Winter Hill gang, and John Connolly ( Joel Edgerton), the FBI agent with whom Bulger formed an alliance, as points of ingress to a true story of desperation, manipulation and corruption.

In the film’s slow unraveling of the poignant, yet subtle, threads that led to the rise and fall of one of Boston’s greatest criminals, Cooper finds plenty of opportunity to chart the emotional tremors of his lead characters, often choosing to study their faces over their actions. Though the core material doesn’t rise too far above that of a typical biopic, Black Mass soars due to the sheer skill of its central performances, pulling the viewer into the lives of two men ruined by their twisted concept of brotherhood.

Bulger is untouchable. Staring into the camera, Depp electrifies the film’s opening minutes with a sizzle that doesn’t die off until the credits roll. Though Bulger is first seen berating one of his men for doubledipping his fingers into a bowl of corn, much of the film’s first half is spent attempting to humanize him, and the effect is profound. There’s a strangely pitch-perfect dissonance in seeing Depp’s Bulger perform acts of kindness: Those eyes remind us of his cruelty, but Depp plays the part with such a genuine veneer that it’s hard not to lend him quiet respect. Seeing these moments of compassion is like watching a spring wind up before its inevitable release, and it’s captivating.

When Bulger does finally strike, his attack is like that of a cobra but with even less remorse. This is a creature willing to shake a man’s hand moments before his execution or, after a particularly shocking murder, remark, “I’m going to take a nap.” The violence in the film is sporadic and quick but packs a punch, partly due to Bulger’s disaffected reaction to his own brutality. For Bulger, there is no distinction between kindness and cruelty, and Depp plays this moral sickness with a slick, icy flair that never overstays its welcome or crosses into melodrama. In fact, compared to his recent performances — which have ranged from entertaining (Pirates of the Caribbean) to bland (take your pick) — Depp is relatively low-key here, electing to underplay when he can. The effect is perfect, making his fleeting outbursts of mania even more terrifying. There were moments where I recoiled in my seat, as if his malice would tear through the screen and freeze the theater. He’s a revelation to watch, and the film’s script gives him a gold mine of memorable moments to play with.

Joel Edgerton plays Connolly with equal fervor. From the beginning, we can see the desperation in his eyes as he does everything he can to set up an alliance with Bulger. In every scene featuring the two of them, it’s clear that Bulger has the power. As the film progresses, this power starts to infect Connolly’s entire life. One of Depp’s best character choices is to move like he’s wearing a suit of armor, filling the screen with his enormous gravitas; eventually, Edgerton has Connolly start to mimic this walk. His new suits and watches, courtesy of his lucrative new alliance, imbue him with a sense of accomplishment. However, the bigger Bulger gets, the more difficult it becomes for Connolly to keep him under control, meaning that Edgerton is placed in the challenging position of seeming both desperate and powerful at the same time. He pulls this off masterfully. A film without such a stellar Connolly might have buckled during the scenes where Bulger is absent, but Edgerton’s performance gives the movie two phenomenal halves that work equally well.

Unfortunately, the film can’t be carried by Bulger and Connolly alone, and though the supporting cast is excellent across the board — Dakota Johnson is particularly affecting as Bulger’s wife — the script could have spent some more time developing the central characters’ spouses. They seem to serve little purpose other than to reprimand the protagonists when they did something stupid — which happened a lot — and the narrative would have had a lot more emotional pull if we knew exactly what the characters were losing when the fallout from the dirty deals hit home. Additionally, seeing more of the relationship between Bulger and his brother Billy, played with an inexplicably excellent Boston accent by Benedict Cumberbatch, would have helped round out the narrative.

As a dual-faced character study, Black Mass succeeds admirably, weaving a nuanced narrative with powerful moments that stick with the viewer long after the credits roll. With skillful directing and a knockout cast, it’s worth seeing for anyone interested in the art of performance — provided you can stomach some very in-your-face moments of violence.