An evil ninja, after being cornered and fatally injured by the police, uses his last breath to transfer his spirit into an unsuspecting telephone linewoman and aerobics instructor, Christie Ryder. Christie quickly becomes plagued by nightmares and strange occurrences as the ninja's spirit begins to take over her life, compelling her to seek revenge on those who wronged him. Amid her daily routine, she finds herself inexplicably drawn to weapons and combat skills she never knew she possessed, bewildering her friends and colleagues.

As Christie struggles to understand the source of her newfound abilities and bizarre behavior, she meets a police officer, Billy Secord, who is determined to protect her and unravel the mystery surrounding her possession. Together, they seek help from a knowledgeable and relentless professional ninja, Yamada, who has his own reasons for stopping the evil spirit. Desperate to reclaim her life and freedom, Christie must confront the dark force within her as the battle between good and evil escalates, leading to a perilous confrontation.