Atom Egoyan’s “Remember” is frustrating, not because it’s necessarily bad but because it wastes an intriguing premise and a great performance by Christopher Plummer and settles for mediocrity. What could have been a superb drama/mystery about denial, repression and confronting the sins of one’s past is ultimately an instantly forgettable thriller with a twist ending.

Plummer plays Zev Guttman, a former Auschwitz prisoner with dementia. A few weeks after his wife’s death, Guttman breaks out of his nursing home, and with the help of another former Auschwitz prisoner, Max Rosenbaum (Martin Landau), who also lives at the rest home, he searches for the Nazi responsible for the death of his family.

“Remember” is essentially a revenge/mystery picture: Guttman buys a handgun and travels to Cleveland, Canada and Boise, Idaho. Egoyan handles the film with restraint and a deliberate pace, and it isn’t dominated by excessive action or violence. Egoyan maintains a consistent atmosphere of suspense.

Is it somewhat ridiculous that an elderly man with dementia could escape from his nursing home, visit multiple states, cross the Canadian boarder, threaten two innocent men and draw nearly outside attention? Absolutely. In fact, Guttman’s son, Charles (Henry Czerny), is somehow unable to get any leads on him. Yet, the narrative remains compelling enough to distract us from these logistical issues.

This may be the first revenge thriller where the protagonist is frail and suffering from dementia. He forgets who he is and where he is, so often that you wonder if he even has the desire for this kind of vigilantism in the first place.

Adding more intrigue is Rosenbaum, who’s orchestrating this trip. He makes travel accommodations for Guttman and provides him the names and addresses of the potential Nazis and a lengthy handwritten letter so Guttman can remember who he is and what his mission is.

Rosenbaum is a manipulator and since we don’t know all the details of what went on all those years ago, it’s unclear as to whether Rosenbaum has any sinister motives or if he simply wants to help him. He spends nearly all of his time confined in his room, looking through old historical documents and photos and frequently talks to Guttman on the phone.

Plummer is in top form. Even at 86, the legendary actor gives a fully engaging and enveloping performance. Guttman may be old and frail, but he’s persistent, never letting his aging body keep him from going on his journey.

But then, that twist ending happens, and the movie jumps off a cliff. It involves a major revelation about Guttman’s past (one he had forgotten) that shouldn’t have been contained in a twist ending.

Instead, Egoyan treats it like the big twist at the end of a bad horror movie.

By not exploring the revelation and the major dilemma it creates for Guttman in greater depth, Egoyan trivializes it and the whole movie, leaving the audience unsatisfied.

Furthermore, the supporting characters are frustratingly underdeveloped. As it turns out, Rosenbaum plays a rather substantial role in the final twist (hence, his mysteriousness), but that doesn’t immediately make his character three-dimensional.

Meanwhile, Charles is basically superfluous; he’s given hardly any substance, and we don’t get a sense of his relationship with Guttman. How does he feel about the revelation? How does he feel about his father’s past? We’ll never know, as both he and Rosenbaum are given scarce screen time.

In the end, “Remember” is just disappointing and leaves a lot to be desired. Christopher Plummer and Martin Landau deserve better.