Brian Gittins is a solitary inventor residing in the scenic rural Wales, where his unusual gadgets rarely function as intended. One fateful day, while rummaging through scrap materials, he stumbles upon a mannequin’s head. This peculiar find ignites his imagination, pushing him to attempt the creation of an artificially-intelligent robot. Unfortunately, his initial efforts yield no results as he cannot seem to activate the invention. However, during a wild thunderstorm that night, Brian's fortunes change when he discovers the robot, now miraculously activated, roaming outside his workshop. He invites the curious creation into his home.
The next morning, Brian is astonished to find that the robot, who names itself Charles Petrescu, has mastered the English language merely by poring over a dictionary. From then on, Brian and Charles share playful moments as Brian introduces his new companion to the property and delights in his innocence. As Charles's inquisitiveness grows, so does his desire to explore beyond their home, but Brian insists that he remain close.
As time passes, Brian finds himself taking Charles along during his handyman work in town, although he keeps Charles positioned safely within the truck. Their secret is on the verge of discovery when Hazel, a woman with whom Brian has developed feelings while working for her mother, sees Charles. Impressed by the robot, she agrees to keep Brian’s secret and joyfully joins them for a walk around a picturesque lake, after which Brian musters the courage to ask Hazel out again.
However, as Charles continues to yearn for the wider world, Brian’s strictness creates a rift between them. Tensions escalate when Eddie, a local bully, along with his two spoiled daughters, finds Charles and attempts to purchase him from Brian. Overwhelmed, Brian firmly declines, but Eddie retaliates by pushing him to the ground. The following day, upon returning home from work, Brian discovers that his front door has been wrenched off its hinges, and Charles has gone missing.
In a frantic search, Brian and Hazel locate Charles at Eddie’s place, but Eddie deceitfully claims that Charles arrived of his own accord. To their horror, they learn that Eddie plans to burn Charles in a bonfire that very night. Heartbroken, Brian and Hazel regroup at his house, where Hazel compliments Brian for his ingenuity in creating Charles, prompting the pair to collaborate on a new project.
Determined to save Charles, Brian and Hazel return to the bonfire just in time for Brian to rescue him from the flames. A chaotic chase ensues as Eddie and his family pursue Brian, Charles, and Hazel into town, where the community comes together to confront Eddie about his misdeeds. Utilizing his inventive prowess alongside Charles, Brian manages to thwart Eddie and send him and his family away.
In the aftermath, Brian comes to terms with Charles's adventurous spirit and presents him with a travel pass, symbolizing his newfound acceptance. As Brian and Hazel bid Charles farewell at the train station, their relationship deepens, marking a new chapter in their lives. The film concludes with a heartwarming montage during the credits, showcasing Charles against the backdrop of monumental landmarks from around the globe as he embarks on his new adventures.
