It's 1942 and the Nazis are determined to prevent Dr. Edwin Conway from giving America his work on developing a jet engine. In Operation Grab Bag, the prequel to Operation Pastorius, Conway and his two adult children were smuggled out of Germany by Frank Sweeney, an American pilot who is now full-time with the O.S.S. The Nazis have sent two U-boats to America. Each sub is sending ashore a team of four men. Their mission is to blow up munition plants, key bridges, and poison the country's water supply. Their efforts are designed to disrupt the American military supply chain, terrorize American citizens, and create doubt as to whether America can win the war in Europe. Two of the saboteurs have been pulled off the main mission and given a new, urgent assignment: eliminate Edwin Conway, thereby crushing America's ability to develop the jet engine technology for its Air Force. Sweeney, who has fallen in love with Leigh Conway, Edwin's daughter, gets involved when an attempt is made on Edwin's life, right before his eyes. Working closely with his father and his boss George Parker, Frank must find Conway's attackers and the local spy who is helping them, all the while trying to determine how deep the Nazi sabotage network runs in America.