In later years, James Cagney regarded White Heat with a combination of pride and regret; while satisfied with his own performance, he tended to dismiss the picture as a "cheap melodrama." Seen today, White Heat stands as one of the classic crime films of the 1940s, containing perhaps Cagney's best bad-guy portrayal. The star plays criminal mastermind Cody Jarrett, a mother-dominated psychotic who dreams of being on "top of the world." Inadvertently leaving clues behind after a railroad heist, Jarrett becomes the target of the feds, who send an undercover agent (played by Edmond O'Brien) to infiltrate the Jarrett gang. While Jarrett sits in prison on a deliberately trumped-up charge (he confesses to one crime to provide himself an alibi for the railroad robbery), he befriends O'Brien, who poses as a hero-worshipping hood who's always wanted to work with Jarrett. Busting out of prison with O'Brien, Jarrett regroups his gang to mastermind a "Trojan horse" armored-car robbery.
~ Hal Erickson, All Movie Guide