The film stars Marilyn Monroe, Joseph Cotten, Jean Peters, and Max Showalter (credited as Casey Adams).

While touring the Falls the following day, Polly sees Rose passionately kissing another man, her lover Ted Patrick.

That evening, Rose joins an impromptu outdoor party and requests that a record of her favorite song, "Kiss", be played.

George storms out of their cabin and breaks the record, suspecting the song has a secret meaning for Rose.

Seeing that George has cut his hand with the record, Polly visits his room to apply mercurochrome and bandages.

George confides that he was a sheep rancher whose luck turned for the worse after he married Rose, whom he met when she was a barmaid.

The next day, Rose lures George into following her to the dark tourist tunnel underneath the Falls, where Ted is waiting to kill him.

To let Rose know that George is dead, Ted will request the Rainbow Tower Carillon play "Kiss."

George has the carillon play "Kiss" again to panic Rose, who flees the hospital, intending to cross the border back to the United States.

When the speedboat moors in Chippawa for gasoline and other supplies, George steals it to try and cross the Canada–United States border, but Polly returns to the boat before he can depart.

Reisch said, "Anybody hearing the name Niagara thinks of honeymoon couples and of some sentimental story of a girl walking out on her husband on their wedding night and their getting together again.

According to Reisch, "we thought that was a nice idea, until there came a second telephone call that he wanted her to be the villainess, not the girl... My God!

[7] Peters' character was initially the leading role, but the film eventually became a vehicle for Monroe, who was by that time more successful.

"After he'd seen it, Zanuck simply couldn't accept the fact that the police at Niagara Falls were of Canadian extraction.

"[6] Henry Hathaway said the film would have been better had his original choice James Mason played the lead male role.

[10] Upon the film's release, A. W. of The New York Times praised the film, if not the acting, writing, "Obviously ignoring the idea that there are Seven Wonders of the World, Twentieth Century-Fox has discovered two more and enhanced them with Technicolor in Niagara... For the producers are making full use of both the grandeur of the Falls and its adjacent areas as well as the grandeur that is Marilyn Monroe... Perhaps Miss Monroe is not the perfect actress at this point.

The camera lingers on Monroe's sensuous lips, roves over her slip-clad figure and accurately etches the outlines of her derrière as she weaves down a street to a rendezvous with her lover.

In 2001, Robert Weston wrote, "Niagara is a good movie for noir fans who crave something a little different.

Be warned, the film was shot in glorious Technicolor, not black and white, but still boasts an ample share of shadows and style....

[15] Rose is a femme fatale, seductively dressed in tight clothes revealing her sensual figure.

[16] In the weeks after Monroe's death in August 1962, Andy Warhol used a publicity photo from Niagara as the basis for his silkscreen painting Marilyn Diptych.