A forgotten airship. A deadly secret. A woman hunted in the skies above. Summer 1930, on the eve of its daring transatlantic flight to Canada, Britain's newly designed R-100 airship becomes the stage for a deadly game of espionage. Mackenzie Gordon, a trailblazing Scottish naval architect, is thrust into Britain’s R-100 program to design urgent replacement parts for the crippled airship—hurling her into a storm of political pressure, national pride, and life-or-death engineering. Her father’s buried past drags her into a web of espionage and betrayal that strikes far closer to home than she ever imagined. As rumours coil through shipyards and the back alleys of Glasgow, Mackenzie uncovers a ruthless smuggling network reaching from Scotland to Berlin. To expose the truth, she must hunt down a shadowy operative known only as Neptune—a double agent whose fractured loyalties could tip the balance of nations. When a trusted family friend urges her to cross the Atlantic to find missing spymaster William Stephenson in Canada, Mackenzie seizes a berth on the R 100. On the transatlantic crossing, she encounters real historical figures—Captain Booth, First Officer Meager, and engineer novelist Nevil Shute Norway—each guarding dangerous secrets of their own. When sabotage strikes, suspicion falls squarely on Mackenzie. To clear her name, she must uncover the truth the same way she builds ships—by reading the stress points, tracing the hidden faults, and locating the single weak joint that could bring everything down. As a deadly white squall builds off Montréal, the R-100 and all aboard hang in the balance. Double Agent Within is a propulsive historical spy thriller grounded in real aviation milestones—a tale of courage, deception, and survival played out on the very edge of history. Some secrets were never meant to be told.