Synopsis: Eliot Ness may have gotten lots of publicity (especially long after the fact) for breaking the Capone mob, but as Joseph H. Lewis' The Undercover Man reminds us, it was the accountants and the numbers-crunchers that brought down Capone and his mob. Frank Warren (Glenn Ford) started out as an accountant, but now serves as an investigator for the Treasury Department. His job has frequently required him to go undercover, masquerading as a criminal to get the goods on the top-level tax-law violators that his unit targets. But now his assignment is to gather evidence on the operations of the nation's number-one crime boss and get proof of the income that he and his lieutenants are not declaring, and this proves not only frustrating but dangerous. Potential stoolies are murdered and witnesses intimidated, and when one otherwise "respectable" lawyer (Barry Kelley) starts mentioning Warren's wife (Nina Foch) in casual conversation, he takes the hint. He's ready to quit until the mother (Esther Minciotti) of a witness-turned-victim tells him about what life was like in Italy under the Black Hand, and why she came to America to raise her sons. Warren and his men (James Whitmore, David Wolfe) make one last attempt to get the proof they need, tracing signatures and handwriting to get evidence implicating a small man in the operation, using it to turn him and going for bigger fish. Finally, even the shyster lawyer who has been dogging Warren every step of the way ends up in the sights of the feds, and the mob turns its attention to getting rid of this new "liability" and taking care of Warren as well.