Allan Mann, an athletic law student, faces a drastic change in his life after a severe accident leaves him quadriplegic. Struggling with his new reality and losing hope, Allan participates in a radical experiment to regain some independence. His friend Geoffrey, a scientist working on behavioral research with monkeys, decides to give him Ella, a specially trained capuchin monkey intended to aid in Allan's daily activities. Initially, Ella's assistance seems to offer a reprieve from Allan's deepening depression, forging a unique bond between man and monkey.

However, as their connection grows stronger, Ella begins to exhibit increasingly strange and violent behavior. Allan starts to experience surreal nightmares and sudden bouts of rage, unable to determine whether these are byproducts of his condition or something more sinister connected to Ella. Tensions mount as the line between animal instinct and malevolent influence blurs, driving Allan to question his own sanity. Gasping for control over his fractured life, Allan must unravel the mysterious bond with Ella before it destroys everything he holds dear.