On July 4, Bobby (Joseph Gordon-Levitt) and Kate (Lynn Collins) are indecisive about what to do for the holiday. They decide to flip a coin and then each takes off in the opposite direction. Two alternate stories unspool.

In Brooklyn, they decide to spend the day with Kate's family. Her mother Sylvia (Assumpta Serna) is disappointed in her and her sister Sophie (Olivia Thirlby), and perhaps that is the reason why Kate doesn't tell her that she is pregnant. She and Bobby have not been able to decide whether to have a child or not. They certainly have nurturing instincts as demonstrated by their tender treatment of a stray dog they find and bring with them. Both of them are baffled by Kate's mother and her negative response to him.

In the other story, Kate and Bobby head to Chinatown. But their plans are upset when he finds a cell phone in a cab and they suddenly find themselves involved in dangerous drama involving big money, a murder, and being chased by a hit man. Manhattan provides the backdrop for their adventure which forces them to elude attack, run for their lives, sleep on a roof, and try to retrieve some payback for all their trouble in returning the cell phone.

Uncertainty is directed by Scott McGehee and David Siegel, and they hold our interest as the two different stories unfold. The key to the film's success is the superb performances by Joseph Gordon-Levittt and Lynn Collins who improvised much of the dialogue. The film certainly reveals the central role in our lives of computers and cell phones. Lynn Collins is remarkably fresh and vibrant as Kate; she is especially good as she struggles with the difficulty of keeping a secret from her parents. In both the domestic drama and the thriller tale, Bobby and Kate's commitment and love are tested.