"The Last Templar" opens in 1291 with the fall of the Latin Kingdom's reign in the Holy Land in Acre. As the burning city is taken by the Sultan's forces, a lone galley escapes out to sea, carrying Martin of Carmaux, a young knight from the historic order of the famed Knights Templar. Also on the galley are Martin's mentor, Aimard of Villiers, and a mysterious chest entrusted to them by the order's dying Grand Master. But the ship never reaches its destination.

The story fast forwards to present-day New York City. During a gala opening night for an exhibition of Vatican treasures at the Metropolitan Museum, four masked horsemen, dressed as Templar Knights, storm into the museum, scattering Manhattan society. Tess watches in silent terror as the leader of the horsemen hones in on one particular piece -- a strange geared device that he grabs as he disappears into Central Park.

As the horsemen's dead bodies start turning up -- and the importance of the stolen device becomes more apparent -- Tess and Agent Daley are drawn into the dark, hidden history of the crusading Knights and of the last surviving Templars' fateful journey from Acre. The pair is soon propelled into a dangerous adventure that takes them into the cemeteries and sewers of Manhattan, across continents, through desolate Turkish highlands and finally into a violent storm on the Mediterranean that shipwrecks them onto a remote Greek island -- and into the very heart of an incredible Vatican secret.