Kiss Me Deadly

Ralph Meeker plays Mike Hammer, a tough Los Angeles private eye who is almost as brutal as the crooks he chases. Mike and his assistant/secretary/lover, Velda (Maxine Cooper), usually work on "penny-ante divorce cases."
One evening on a lonely country road, Hammer gives a ride to Christina (Cloris Leachman), an attractive hitchhiker wearing nothing but a trench coat. She has escaped from a mental institution, most probably the nearby Camarillo State Mental Hospital. Thugs waylay them and Hammer awakens in some unknown location where he hears Christina screaming and being tortured to death. The thugs then push Hammer's car off a cliff with Christina's body and an unconscious Hammer inside. Hammer next awakens in a hospital with Velda by his bedside. He decides to pursue the case, for vengeance, a sense of guilt (as Christina had asked him to "remember me" if she got killed), and because "she (Christina) must be connected with something big" behind it all.
The twisting plot takes Hammer to the apartment of Lily Carver (Gaby Rodgers), a sexy, waif-like woman who is posing as Christina's ex-roommate. Lily tells Hammer she has gone into hiding and asks Hammer to protect her. It turns out that she is after a mysterious box that, she believes, has contents worth a fortune.
"The great whatsit," as Velda calls it, at the center of Hammer's quest is a small, mysterious valise that is hot to the touch and contains a dangerous, glowing substance. It comes to represent the 1950s Cold War fear and paranoia about the atomic bomb that permeated American culture.
Later, at an isolated beach house, Hammer finds "Lily," who has been revealed to be an imposter named Gabrielle, with her evil boss, Dr. Soberin (Albert Dekker). Velda is their hostage, tied up in a bedroom. Soberin and Gabrielle are vying for the contents of the box. Gabrielle shoots Soberin, believing that she can keep the mysterious contents for herself. She also shoots and wounds Hammer, who manages to find Velda. As Gabrielle slyly opens the case, it is ultimately revealed to be stolen radionuclide material, which in the final scene apparently reaches explosive criticality when the box is fully opened. Horrifying sounds emanate from the nuclear material as Gabrielle and the house burst into flames just as Hammer and Velda escape.
Alternative ending[edit]
The original American release of the film shows Hammer and Velda escaping from the burning house at the end, staggering into the ocean as the words "The End" come over them on the screen. Sometime after its first release, the ending was altered on the film's original negative, removing over a minute's worth of shots where Hammer and Velda escape and superimposing the words "The End" over the burning house. This implied that Hammer and Velda perished in the atomic blaze, and was often interpreted to represent the apocalypse. In 1997, the original conclusion was restored, where Velda and Mike survive. The DVD release has the original ending, and offers the truncated ending as an extra.
The movie is described as "the definitive, apocalyptic, nihilistic, science-fiction film noir of all time â at the close of the classic noir period."[4]

Question: How is the movie described?