Mace Sowell [Patrick Stewart] is a retired DIA agent who believes his life is in danger from his former boss, Admiral Thomas Michelmore [Richard Livingston], who is now running for President of the United States. Mace holds information about covert DIA dealings that could derail Michelmore's campaign if it becomes public. The data sits in cyberspace and is set to be released to major newspapers across the western world unless Mace can remotely reprogram the mail server every 24 hours using a password only he knows. Complicating matters, Mace is in the early stages of Alzheimer's and struggles to convince others that his threat is real rather than a product of paranoia.
Because he rarely leaves home and only does so in disguise, he visits his psychiatrist Dr. Simon [Héctor Elizondo], a visit arranged under pressure from his daughter, Michelle Sowell-Ross [Joy Kilpatrick], who threatens to have his mental competency evaluated. Since Mace never discussed his DIA career with his family, and because paranoia is common with Alzheimer's, he cannot persuade Dr. Simon or Michelle of the danger. Dr. Simon suggests a practical path: hire an in-home caregiver or pursue commitment if his behavior becomes unmanageable.
Following a difficult search, Michelle hires Andi Travers [Kimberly Williams-Paisley], whom Mace immediately resents. Their relationship starts tense as Andi pushes for lifestyle changes, including a macrobiotic diet, and Mace resents the invasion of his privacy as part of his background check.
Mace has a small circle of friends, including Stu, [Craig Shoemaker] as Stuart Bittenbinder, a pool cleaner who does odd jobs for him. Stu explains he has known Mace since before the onset of his dementia. Among the tasks he performs are drills in which Stu dresses in quasi-military gear and simulates breaking into Mace's house. Andi mistakes one drill for a real burglary and injures him with a golf club, later covering the incident from Michelle during a phone call.
As Mace and Andi slowly find some footing, he stages a car-bomb removal in Michelle's van, prompting her to disallow further drills. After Mace accuses Andi and Stu of conspiratorial antics, they attempt a final drill to lift his spirits, but his subpar performance suggests he is no longer able to fend for himself.
Mace grows more dependent on Andi, yet remains convinced Michelmore is trying to kill him. He even shoots at a neighbor's incoming car, a move that leads Michelle to remove all weapons from his home and to pursue a competency hearing. Facing commitment, Mace reveals to Andi his information on Michelmore and the secret of his dead man's switch, and bribes her into aiding his escape from the country.
That night, Mace finds Andi attempting to abort the dead man's switch and trails her to her home the next morning. Sneaking inside, Mace discovers that Andi is an agent of Michelmore. Back at his own home, Mace expresses admiration to Andi for being able to fool even him. As Andi shoots and kills a passing Stu, Mace shoots her, but is wounded himself in the process. In his last act of clarity, Mace sets off the dead man's switch and calls to report Andi's dead body, but finds that he is unable to remember his own name.
