Ryan Reynolds as Kevin, Kristin Booth as Sam, and Joris Jarsky as Rob play a game they call Foolproof, in which they craft detailed, working blueprints to infiltrate and burgle various targets. They do not actually execute the heists; instead they simulate them, relying on the same technical and physical abilities needed to pull off the jobs. They adhere to strict rules: they must use identical equipment and infrastructure as the target, and they forbid firearms of any kind, a discipline they treat as a kind of intellectual sport rather than a crime.
A famous criminal, David Suchet as Leo Gillette, breaks into Sam's apartment, steals the trio's jewelry-warehouse heist plans, and executes the job. He then uses those same plans to blackmail the group into designing and executing a plan to steal $20 million in bonds from a bank. The ultimatum hangs over them, turning a playful exercise into a dangerous obligation and testing the trust among the three friends.
Tension escalates as Rob grows closer to Leo, Sam uses her physical prowess to push Leo’s limits and is occasionally punished for it, and Kevin destabilizes the growing risk by trying to protect the trio and minimize their exposure. Leo rewards Rob by paying him alone for the trio's involuntary help in the successful jewelry heist, a move that deepens the fissure between the partners and shifts the balance of leverage within the group.
To escape the blackmail, Kevin and Sam break into Leo's restaurant wine cellar to obtain the plans being used to coerce them, but Rob informs Leo, who has his goons keep a careful eye on them. The trio proceeds with meticulous planning for the bank job, and the operation initially proceeds smoothly: they replace the bonds with forged ones to avoid detection and set up contingencies for any possible snag.
Yet the plan fractures when Leo and Rob turn on Kevin and Sam, leaving them to fall with a crashing elevator car. In the ensuing standoff, a fallen Sam shoots Rob and Leo shoots Sam, leaving Leo convinced he is the last one standing and prompting a desperate escape with the bonds. He returns to his restaurant only to find it swarmed by firefighters and police, a blaze sparked by a device Kevin had left in the wine cellar.
The authorities seize the moment to press Leo, confronting him with a strongbox that originally held both the jewelry heist plans and the diamonds. A quick search exposes his possession of the stolen bonds and a handgun recently fired, loaded with blanks. Dressed as a firefighter, Kevin slips through the cordon and into a car with Sam and Rob, revealing that he has recovered the plans used to blackmail them and the diamonds. They drive away together, discussing what comes next and the uncertain future ahead, bound by their shared experience and the fragile balance of their partnership.
