From the publisher's introduction:
"Call of Duty" is a Call of Cthulhu scenario set in the fictional city of Durban, Rhode Island, in the year 1925. The investigators play agents from the Federal Bureau of Investigation trying to shut down Antonio Marchesi's illegal operations, which include nefarious acts such as bootlegging and the release of Gods from beyond space and time. So! Pull down your fedora, check your badge, load another drum in your Tommy Gun, and get ready to put your sanity to the test―your superiors will never believe this.