Heading in to Luce, I knew next to nothing about it. Based on the title alone, I might have guessed that the main characters were named "Henry" and "Clare Boothe".

In fact Luce is a contemporary drama, based on the 2013 play by JC Lee (who cowrote the film's script, which nicely opens up the story for the big screen, with director Onah). It is also the name of its main character (played by Kelvin Harrison Jr.), an uncomfortably charming teenager whom everyone adores except for his apprehensive history teacher Ms. Wilson (Octavia Spencer in fine form). What is Ms. Wilson's problem with Luce? And how much does Luce deserve her suspicions? From the first shot of the film to its last, we are invited to ponder this second question.

Luce, an African immigrant who now speaks perfect American English, was born in war-torn Eritrea, where he witnessed untold horrors until a liberal white American couple adopted him at the age of seven and raised him in their tony Arlington, Virginia home. (Naomi Watts and Tim Roth play Luce's parents; their previous pairing, in 2007's sadistic Funny Games, subtly informs Luce's uneasy tone.) Now a senior in high school, Luce is headed towards valedictorian status, captain of the track team, and an Ivy League future. But from the moment we meet him, we are on guard. He's too friendly with adults, too easy with his lines. There's something phony about him. If this were a sci fi movie, you'd swear he was an alien or an android. (Luce is also reminiscent of Six Degrees of Separation.) But when we spend time alone with him, or see him interact with his friends, we see that Luce is more complicated than we first thought – and so is the film.

A plot does develop out of Luce and Ms. Wilson's mutual disdain for each other, but we're never let in on the whole truth. That makes the film a thriller, though not in the traditional sense: there are no breathless chases or battles to the death here. Yet in filling us with doubt about its titular character, Luce keeps us on edge. It's an unsettling look at what it means to be a "model black" in today's America, and how this compounds the pressures from parents and school that gifted teens already face. If we can't trust Luce, it's because he has no clue about who he's supposed to be.

Onah shoots his film like a modern French drama: chilly and straightforward. The cast is marvelous and the story is bound to incite conversation. While the film falters a little in a climactic monologue for Spencer that feels too on-the-nose, I otherwise enjoyed its commitment to ambiguity.