‘Complete Unknown’: Skilled cast squandered on a meager premise

There is bit running through the first third of “Complete Unknown” in which Tom, one of the main characters, is celebrating his birthday and insists repeatedly to his guests that later that night they will go dancing.

Sure enough, they go. And Tom never dances.

It’s the perfect representation of Joshua Marston’s film, though he probably wouldn’t see it that way. Much is promised and too little is delivered.

What is delivered are intense performances by two terrific actors, Michael Shannon as Tom and Rachel Weisz as Jenny, a mysterious woman who makes a surprise reappearance in his life that sets the film in motion. Happily, they have a lot of scenes together, bouncing old wounds and tentative longings off one another.

Sadly, you kind of wish they were doing something else.

Marston (“Maria Full of Grace”) throws us off-kilter at the start, in a good way — we see Weisz touring an apartment with a potential new roommate, working as a magician’s assistant, helping a patient as a nurse in a hospital and more. We get no explanation for any of this, just a final shot before the opening credits of her swimming in the ocean, not long after telling the would-be roommate she can’t swim.

What is going on here?

We’ll find out, and quicker than we might expect. However, you won’t find out here, at least not much; the mild-ish surprises the film contains are best left for your discovery.

We meet Tom working in a New York office, laboring over an e-mail about some kind of legislation involving grazing trends, and since he’s played by Shannon he is doing so with complete and utter concentration.

Tom has lunch with his co-worker, Clyde (Michael Chernus), and they’re spotted by Jenny, who is working as a biologist studying frogs. Later she and Clyde flirt, and eventually they go to Tom’s birthday party together.

The party is filled with tension even before it starts. Ramina (Azita Ghanizada), Tom’s wife, has been accepted into an elite jewelry-making program in California. Tom, while supportive, isn’t sure he wants to accompany her. He may prefer sticking around to present his leaden presentation for the grazing-trend legislation. They’re still talking about it — or at least she is trying to, while he avoids the conversation — when guests arrive, Clyde and Jenny among them.

Only now she is Alice.

The birthday dinner takes up a considerable chunk of the film, as standard dinner conversation turns uncomfortable, especially when Alice starts talking about how she once simply up and left her life, never going back.

Tom is the most-uncomfortable of all, and he bores in with occasional squirm-inducing questions. The mystery will mostly be solved with more than half of the movie left.

Eventually they’ll all go dancing, but Tom and Jenny — she’s no longer Alice — engage in intense conversation. They end up outside, where a chance meeting with a woman (Kathy Bates) leads them back to her apartment, where she and her husband (Danny Glover) live. Again, watching the actors is what makes the scene worthwhile; due to the nature of the story, it could exist almost as an acting exercise.

Confused enough yet? It’s really more straightforward than tortuously trying to avoid giving away too much makes it seem. If anything, in fact, “Complete Unknown” is too straightforward, offering up its secrets too early, without making us care enough about what leads to the answers.

Director Joshua Marston is scheduled to participate in a Q&A after Friday’s 7:20 p.m. screening at Landmark’s Century Centre.

Bill Goodykoontz, USA TODAY Network

★★

Amazon Studios and IFC Films present a film directed by Joshua Marston and written by Marston and Julian Sheppard. Running time: 90 minutes. Rated R (for some language). Opens Friday at Landmark Century Cinema.