Willem Dafoe defies classification. He appears in blockbusters and arthouse films, in lead roles or as part of an ensemble. What can be counted on is that he’ll add a dash of idiosyncratic malevolence to whatever part he’s playing. Whether he’s playing Christ, Antichrist or somewhere in between, there’s always something slightly off that makes him watchable. In “Inside,” director Vasilis Katsoupis provides him with a showcase part in what is essentially a one-man show that Dafoe carries with aplomb.

Dafoe’s character is an art thief named Nemo. He is first shown breaking into a high-tech Manhattan apartment. He’s connected to someone on the outside via microphone. It’s clear they hacked into the apartment’s security system. The camera slowly reveals the apartment as an expensive and impeccably designed but sterile abode. Its colors are monochromatic in a mostly bluish hue, there’s an indoor pond and plants that look plastic. The few pops of color come from the art on the walls. Nemo’s there to steal a valuable Egon Schiele portrait which he can’t immediately locate. As he looks around the vast space, inspecting the many pieces of art, the security system malfunctions. He’s trapped inside this gilded cage. Before long he realizes that his cohorts are not coming to save him. Nor is anyone else. He’s on his own.

Katsoupis, collaborating with Ben Hopkins, has devised a clever way to examine the world of art collectors. They are aided by the bold stark lighting of Steven Annis’ camera and the open aseptic space designed by Thorsten Sabel, which eerily represents a cage. In voiceover, repeated a couple of times, Nemo recalls an exercise he was put through as a child in school. Asked what he’d save in a fire, he responded with his most precious possessions. Here he is surrounded by many beautiful and expensive pieces of art, yet what he longs for is a connection with another human being. Any person would do.

Katsoupis and Hopkins critique the world of art collectors and how it has become a race for possession without regard to how or why the art is made. By showing Nemo’s plight, they manifest this crisis of faith into one man’s need to connect — and more importantly, to survive. (Via the security cameras, he spies on and begins to fantasize about a cleaning woman, played by Eliza Stuyck, even going so far as to sketch her at one point.)

Dafoe’s an inventive and agile character actor, handsome and appealing but also possessing distinctive malleable features. All this makes him perfect for this one-man show, as he’s never less than immensely watchable. He’s called upon to telegraph Nemo’s emotional state through his body. Images of his back and hunched shoulders fill the frame. He’s shown on the floor in the fetus position and the camera patiently closes up on the creases of his neck and hands. His body becomes a canvas for the filmmakers to convey not just the loneliness of the character but also the unnecessariness of collecting art as possessions. All these beautiful pieces cannot sustain Nemo in any way.

Halfway into a mostly silent performance, Nemo playacts as if he’s a cook in a TV show. His solitary existence drives him to talk back to the security footage on the TV. What a welcome relief to hear Dafoe’s voice and see him animated with emotion. Finally he gets to do something other than the silent poses he has been doing for most of the running time. In so doing, “Inside” reveals what’s been absent all along.

With this premise, there’s ultimately no place to go. As the story unfolds, the audience feels as stuck as Nemo, with no escape in sight. The film has exhausted both the premise and its leading man’s capabilities, while the audience has grown tired of pondering whatever themes it purports to examine. It’s time to part ways, and yet the images keep flickering on screen and the film keeps going. “Inside” has an intriguing premise and an actor who makes whatever’s thrown at him intriguingly watchable. What it lacks is sufficient sense of who this character is, and a resonant enough narrative to justify being locked up together.