Michael Fassbender was already on Hollywood's map when Fish Tank came out in 2009. But Andrea Arnold's film served as a perfect calling card for how simultaneously charming and frighteningly intense he could be. Fassbender had earned his serious actor chops the year before by dropping a scary amount of weight for his memorable, steely work in 2008's Hunger. Later in the year, he'd turn in an unfortunately brief but devilishly fun appearance in Inglourious Basterds.

But the story of Fish Tank hinges entirely on Fassbender's onscreen presence. Though it's focused on troubled 15-year-old Mia (a terrific, raw performance from first-time actress Katie Jarvis), it's Fassbender's Connor who propels the story. Connor is a surprisingly stable new boyfriend for Mia's mother and manages to draw the withdrawn Mia out of her shell a little bit, encouraging her interest in dancing and catching a fish with her on a day trip.

All the while, there's a gnawing sense of danger to Connor and Mia's friendship. As she did in the Academy Award-winning short Wasp and her feature debut Red Road, Arnold is exploring working class life in Britain with as little varnishing as possible, and Mia's life on a council estate (housing project) in East London seems to mark her for doom. Her mother, who is in her early 30s, clearly had her as a teenager, and is largely absent as a role model, intending instead to send her to a boarding school geared towards "ASBOs" (a British label for kids who indulge in anti-social behavior) which would certainly be a horrible place.

Mia is granted moments of tenderness—she worries about a horse chained up by a traveler community and repeatedly tries to free it—but they are brief, and she is a largely inscrutable young woman. Even in her scenes with Connor, she mostly plays it cool, but the audience is at least aware of the impact his attention has on her. In the hands of a different actor, Connor would come across as a garden-variety creep—something that could be said of a lot of Fassbender's roles. As he does with sex addict Brandon in Shame, or Magneto in the X-Men films, or even the monstrous Edwin Epps in 12 Years a Slave, Fassbender finds relatable humanity where on paper very little should exist.

The amazing ploy of Fish Tank is that Connor and Mia's relationship doesn't feel entirely predatory on either end (Mia is hardly some young siren looking to snare an older man, although spite for her mother certainly plays a part) although it is undoubtedly destructive. And for all of Fassbender's charm, you're constantly waiting for things to turn sour with Connor. He has an air of darkness no matter who he's playing. It's hard to imagine Fassbender appearing in a light, airy romantic comedy, although perhaps he's versatile enough to shake his darkness.

Of course, things do go wrong. Though no one ends up dead, in prison, or even knocked up (sadly plausible roads this film could have taken), Connor certainly proves himself as tragically flawed and stupid as you could have feared. Mia, of course, makes plenty of horrifying mistakes herself, but since she's young we're so deep in her headspace, it feels much more forgivable.

This is another aspect of the genius of Fassbender's performance. In the first two thirds of the film, Mia is attracted to Connor, and since the audience is on her level more than anyone else's, Fassbender dials up the charm perfectly. As the relationship starts to curdle, Fassbender subtly shifts to a darker persona, although it's not drastic enough to feel hacky. The audience suddenly wants to be rid of him, just as Mia does, once he's revealed to be as pathetic as everyone else in her life.

After Fish Tank and Inglourious Basterds in 2009, Fassbender's career instantly exploded. His 2010 efforts in Centurion and Jonah Hex were likely filmed beforehand, but starting in 2011 he was in everything, from big-budget tentpoles like Prometheus and X-Men, to roles for A-list directors like David Cronenberg (A Dangerous Method) and Ridley Scott (The Counselor), to his continually fruitful collaborations with McQueen.

Fassbender has not, it's true, broken out of the "dark and brooding" box films like Fish Tank put him in. And that could prove a risk the more films he's in, since audiences will quickly get sick of more of the same. But if there's one actor that can avoid diminishing returns, it's Fassbender, who within six years of his first starring role now feels overdue for an Oscar win. Perhaps 2015's Macbeth, the most dark and brooding role of them all, will prove a fruitful culmination of that work.