Riley Fitzhugh is temporarily made officer in charge of the naval guard on board the SS Carlota, a merchant ship assigned to deliver bombs and aviation fuel to the Sebou River during Operation Torch. The Atlantic crossing was supposed to be in convoy, but Carlota breaks down after surviving a U-boat attack and is forced to limp along alone.

At the mouth of the Sebou River, Riley rejoins the Nameless, an anti–U-boat vessel, which has come down from her refit in Scotland to join the Torch attack. When the Nameless is tasked with delivering a company of Army Rangers to capture the French air force base, she and her crew must force their way through the boom guarding the mouth of the river and pass through the gunfire from the French fort on the hills above. Along the way, Riley runs into an old flame or two—one an enemy agent, the other a war correspondent from Cuba.