According to the narration and prologue, this was based on a true story. The film depicts the 1932 murder of a police officer in a speakeasy in Chicago. In 1933, two men were given life sentences for the murder. The action of Call Northside 777 starts out eleven years later, in 1944. Lee J. Cobb, editor of the Chicago Times, comes across a small ad in the classifieds offering $5,000 to whomever can offer information regarding the murderer of the police officer in 1932. Anyone with information is urged to call Northside 777. Cobb is intrigued that someone would be offering so much money for an eleven year old, solved murder, and why it is in such an inconspicuous ad? He has a hunch that there is a story in there and he assigns lead reporter, James Stewart, to the case.

Stewart is at first uninterested but as he thinks out loud and asks questions, Cobb urges him to investigate and see what he can come up with. Stewart starts with meeting the owner of the classifieds ad, who turns out to be the mother of one of the men put in prison for the murder. She is adamant that her son is innocent, and has scrubbed floors since his imprisonment to save up the reward money and pay for the ad.

As Stewart interviews more people investigated in the case, and reviews more news stories and documents related to the case, he realizes that the man in jail for this crime may really be innocent. Noir mainstay Richard Conte stars as the (allegedly) wrong-fully convicted man. Helen Walker has a small but effective role as Stewart's devoted wife whom he confides in when he's trying to figure out the case. They also work on a jigsaw puzzle together throughout the film, which very skillfully acts as a metaphor for what Stewart is trying to do in his work life.

Betty Garde plays the eyewitness whose inconsistent ability to pick out the murderer in the lineup comes into question by Stewart. She is very bitter and uncooperative towards Stewart, and obviously afraid of something or someone unnamed, so he's forced to undermine her credibility and go without her assistance in clearing the man whom he feels was wrongfully convicted.

I thought Stewart was excellent in his role as the everyday man whose work could affect the lives of many people associated with the case. Lee J. Cobb was authentic in the role of Stewart's boss who urges him to keep going in his investigation. I do get the sense though that Cobb is just trying to increase readership in the newspaper, and that he couldn't care less about Conte's character. But Stewart is the one with a little more humanity who is more about solving the crime than increasing readership of his newspaper.

One thing I thought was interesting about this film was that the man who administers the lie detector test to Conte is the actual inventor of the lie detector test.