Call to Arms begins 11 days after the bombing on Pearl Harbor December 7, 1941. It follows the career of Second Lieutenant Kenneth McCoy and the people and events that touch his life in the months following the bombing on Pearl Harbor. Second Lieutenant Kenneth McCoy is wounded fighting in Shanghai just before the bombing on Pearl Harbor, ending up with the nickname "Killer McCoy." He is sent back to the States, and is ordered to spy on a Colonel Carlson, who has strong ties to the President's son, James Roosevelt. Colonel Carlson is gathering a group of elite fighters, similar to the British Commandos, to be called the Raiders. General Lesterby and Colonel Wesley are concerned that Carlson is a communist, crazy, or both, and they worry about what that could mean for the Marine Corps. They send McCoy to spy on Carlson and to find proof that their suspicions are correct.

McCoy is dating a woman named Ernest "Ernie" Sage, who he met through mutual friend, Second Lieutenant Pickering. McCoy refuses to marry Ernie because he does not think that a Marine officer about to be sent over seas should be married. However, she does move to San Diego with him, where he is stationed during his Raider's training.

McCoy is impressed with everything Carlson talks to him about, and thinks he is a good Marine. He enjoys being a part of the Raiders. He and Zimmerman are important parts of the training of the volunteers, getting the weapons and helping making the strategic plans. The Commandant finds out about the plan to discredit Carlson and that his name was used to recruit the key players and quickly and quietly puts and end to it. Hoping that he stopped it before Carlson caught wind of it, theCommandant sends Major Banning to find out how much if anything Carlson knows. His findings were that Carlson had most likely heard the scuttlebutt, but did not know that McCoy was the spy. Banning, knowing McCoy from Shanghai, knew that McCoy was not happy about having to spy on another China Marine and vowed to try to get him out as soon as possible. Banning came though and got McCoy a transfer out as a linguist, but McCoy wanted to stay and be with Carlson on their first mission as Raiders. Carlson and McCoy had a successful mission on Makin Island, and upon their return Carlson signed McCoy's transfer. When Carlson was leaving he told him to tell Rickabee, which was McCoy's contact during his mission, he said hello. McCoy immediately knew Carlson had known all along that he was the spy. Carlson said, "You're a Marine officer. A good Marine officer. And good Marine officers do what they're told to do, to the best of their ability."