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 aboard the R-100. On the crossing, she encounters real historical figures-including 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 stress points, tracing 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 everyone aboard-hangs 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.