The picture is based on a novel by Frank H. Spearman and a previous 1926 film adaptation starring H.B. Warner in the title role, with Lillian Rich, Lilyan Tashman, John Bowers, and Eugene Pallette as supporting cast.
The bad Barton boys—Blake, Leroy and Gabby—rob a train and shoot a guard. Luke Smith, known as "Whispering" to some for his quiet, sly ways, is a detective for the railroad, sent to investigate.
Murray Sinclair, an old friend of Smith's, is in charge of the railroad's wrecking crew. He's glad to see Smith, who shoots Leroy and Gabby and is saved when a bullet is deflected by a harmonica in his pocket, given him long ago by his sweetheart Marian, who is now Sinclair's wife.
It saddens Smith to find out that Sinclair might be in cahoots with Barney Rebstock, a rancher with a bad reputation. Rebstock has been hiding the remaining Barton brother, Blake, who is tracked down by Smith.
Whitey DuSang is a hired gun for Rebstock, who wants to see Smith dead. When the railroad's boss gives Sinclair an order, Sinclair rebels and is fired. Rebstock hires him to pull off a string of daring train holdups.
Smith forms a posse. Whitey kills a guard and betrays Rebstock, shooting him. Sinclair is wounded. Smith does away with Whitey but gives his old friend Sinclair a last chance. When Sinclair rides home, he finds Marian packing and strikes her, accusing her of leaving him for Smith.
Smith shows up and Sinclair apologises for his actions. He seems sincere, but when Smith's back is turned, Sinclair pulls a hidden gun. Before he can fire, Sinclair falls over and dies. Smith leaves town, his work there done.Alan Ladd as Luke "Whispering" Smith
Robert Preston as Murray Sinclair
Brenda Marshall as Marian Sinclair
Donald Crisp as Barney Rebstock
Fay Holden as Emmy Dansing
William Demarest as Bill Dansing
Murvyn Vye as Blake Barton
Frank Faylen as Whitey Du Sang
John Eldredge as George McCloud
Ward Wood as Leroy Barton
J. Farrell MacDonald as Bill Baggs
Will Wright as Sheriff McSwiggin
Film versions of the novel had been made in 1906 and 1926. Paramount had silent rights to the novel from the 1926 film, made by an associated company, and acquired sound rights. The film was announced in early 1947 as a vehicle for Alan Ladd. It was Ladd's first Western and his first movie in colour.
The script made a number of changes to the original novel including changing the double love story to one.
Brenda Marshall was given her first screen role in four years. Filming began on 14 April 1947.
The role of Whispering Smith was partly based on Jake Lefors. The part of Murray Sinclair, Smith's friend who turns to crime, was supposedly inspired by Butch Cassidy.
The filmmakers built a Western town on five acres of the backlot at a cost of $70,000. It included 2000 feet of railroad track on which authentic 1870 locomotives owned by Paramount were operated. The trains were converted from their original wood-burning fuel system to oil. The set was later re-used in many later TV shows and films, including Bonanza.
The film was not released until 1949, by which time Paramount had made and released another Ladd film, Beyond Glory.
The film was a popular with audiences. According to Variety it was the 20th most popular film in the US and Canada in 1949.
Sol Lesser, who had rights to ten Whispering Smith stories, wanted to film some of them with Robert Mitchum. These films were not made. However, Audie Murphy later starred in a Whispering Smith TV series.