Nathan Caine is an unassuming introvert, afflicted with congenital insensitivity to pain and anhidrosis (CIPA), working diligently as an assistant manager at a credit union in sunny San Diego. His co-worker, Sherry Margrave, has developed romantic feelings for him, but Nathan's lack of experience with women and his unique condition make him hesitant to open up. One evening at a bar, Nathan unexpectedly encounters his middle school bully, who cruelly taunts him with the nickname "Novocaine." In a show of support, Sherry seeks revenge by tricking Nathan into drinking a shot filled with hot sauce, and the two share a memorable night together.
On Christmas Eve, their budding connection is abruptly shattered when a group of robbers dressed as Santa Claus—led by Simon Greenly—storms the credit union and takes Sherry hostage. Driven by desperation, Nathan impulsively steals a police car to chase after the vehicle holding Sherry, only to mistakenly follow the wrong car. This error leads him to a confrontation with another robber, Ben Clark, in a restaurant kitchen, where Nathan finds himself in a life-or-death situation. Ultimately, Nathan shoots Ben dead but not before suffering a severe burn on his hand while retrieving Ben's weapon from a deep fryer.
Determined to find Sherry, Nathan notes Ben's tattoo and tracks down the artist, Zeno, hoping to extract Ben's address from him. After a rough encounter, Nathan manages to obtain the information and places a call to his only friend, Roscoe Dixon, a gamer he has never met face-to-face, to help him locate Ben's home. However, when Nathan arrives, the house is rigged with traps, leading him to get caught in a snare. In a moment of panic, he reaches out to Roscoe for help. As Nathan endures torture at the hands of Ben's brother, Andre, he pretends to feel pain, surprising them both when Roscoe arrives and the two manage to turn the tables on Andre.
Things escalate further when police officers, Mincy Langston and her partner Coltraine Duffy, respond and arrest Roscoe, who had changed clothes with Nathan in a bid to avoid detection. Nathan eventually discovers Sherry's shocking connection to the heist, revealing that she is not only Simon's sister but also an accomplice in the robbery. Initially, Sherry aimed to seduce Nathan to learn the bank vault code, but complications arose when genuine feelings surfaced. The situation intensifies as Simon attempts to kill Nathan, but Coltraine intervenes, leading to a violent altercation where Simon shoots Coltraine and escapes with Nathan in an ambulance.
In a dramatic turn, Sherry manages to free herself from handcuffs and gives chase to the ambulance. Once Nathan gains consciousness, he breaks free as well and confronts Simon, leading to a nail-biting struggle where Nathan injects himself with adrenaline to regain the upper hand. In a harrowing finale, Nathan defeats Simon, delivering a lethal blow before collapsing, finally succumbing to his injuries.
Two weeks later, Nathan awakens in a hospital to find that rather than serving a long prison sentence, he has been sentenced to six months of house arrest owing to his heroism in saving Coltraine's life. Fast forward a year, Nathan visits Sherry, who is nearing the end of her own sentence for her part in the robbery. They share a cherry pie, a symbol of their evolving relationship, which Nathan is experiencing for the first time, thanks to Sherry's influence on their first date. As prison guards lead Sherry back to her cell, Nathan takes a bite of the pie, savoring the moment with a smile, hinting at the bittersweet nature of their journey together.
