Casey (Jesse Eisenberg), a meek and timid man, is attacked at random on the street. He subsequently enrolls at a local dojo led by a charismatic and mysterious sensei (Alessandro Nivola), in an effort to learn how to defend himself.

What he uncovers is a sinister world of fraternity, violence and hypermasculinity and a woman (Imogen Poots) fighting for her place in it. Casey undertakes a journey, both frightening and darkly funny, that will place him squarely in the sights of his enigmatic new mentor.