A Top Secret mission is devised by the CIA and Joint Chiefs of Staff on orders from the President to deliver arms to Sandonesia, an African republic about to be invaded by its Communist neighbor. The covert plan is not revealed to the Congress or any government department or agency. A U.S. Navy crew, personally selected by the Chief of Naval Operations, and led by Captain Garrison, uses a merchant ship named Orion for the voyage. Garrison is reticent and confides in no one regarding the mission. His executive officer, Commander James Reed, soon realizes this is not going to be another routine cruise. Reed starts to worry as soon as the Orion sails. Operators in the radio room are frustrated by strange messages arriving over a mystery channel that can only be decoded by the captain. The dispatches do not conform to naval regulations or procedures and the operators never see a file copy of the decoded version. Navigator Howard Burnam has his own dilemma because he does not know where they are going. The captain has drawn a course line across Burnam's paper ocean that ends short of the Azores. Burnam is told to keep the Orion on that course till further notice, which leads him to believe the Azores is not their next port. To the officers, Captain Garrison appears to have become a different man after taking command of the old freighter. Once gregarious, he is now aloof and can never be found during a crisis. He is absent from the bridge during a violent storm that nearly tears the ancient cargo ship to pieces. Reed cannot find him later when a paint locker fire threatens to cause extensive damage. Reed wonders why Garrison appears to have dismissed the welfare of his crew, when he had previously been very concerned about morale. The accidental death of communications officer Lieutenant Bob Morris turns out to be murder when the body is examined by Chief Hospitalman Fletcher, whose experience includes many years in the pathology department at Bethesda Naval Hospital. Below decks, Chief Thompson has his hands full trying to keep peace among the sailors who are on the verge of committing mutiny or jumping overboard. They suffer through sweltering days and nights in their quarters after spending boring hours on watch or some tedious job. Nearly a week into the voyage Reed is stunned by what he finds during an inspection of the ship's cargo hold, but does not tell his fellow officers. He is completely bewildered and now has no clue about why they are sailing the Atlantic on a course to nowhere. Then Captain Garrison suddenly changes course to the north, but still won't reveal their destination to the navigator. An explosive climax occurs on the high seas when the Orion is torpedoed by a Russian frigate--after Captain Garrison boards the warship. As the Orion is sinking, James Reed is knocked unconscious by falling debris. He awakes in a hospital room where a debriefing provides all the answers to his questions about the Orion's strange journey.