Brandon (Michael Fassbender) is a successful, handsome thirty-something living and working in New York. He seems to have it all, but he also has a compulsive personality that has him feeling trapped.

With a ferocious sexual appetite, Brandon survives on a diet of random physical encounters. Sometimes he pays, sometimes he finds satisfaction alone, but one way or another his desires need to be met.

Into his otherwise ordered world comes his sister, Sissy (Carey Mulligan), a troubled young woman who has been left as damaged as Brandon by their childhood which is never completely revealed.