A dramatic tale of spying and espionage, On Secret Service chronicles the Civil War from its onset to Lincoln's assassination. Jakes follows the romance of two couples, divided by war and allegiance. Lon Price is a Pinkerton detective assigned to the railroad out of Chicago. Lon ends up helping in the Union war effort when Pinkerton pledges his company and his men to General McClellan, the early Union hero. Lon falls in love with Margaret Miller, daughter of a wealthy Baltimore publisher with Secessionist sympathies. Margaret is to wed Donal McKee, but Lon arrests her as a spy -- she is a member of Rose Greenhow's inner circle. She is visited by Lon in the Old Capitol prison, and slowly falls for him, too. Lon goes behind enemy lines and makes the mistake of visiting the now-married Margaret, and he suffers greatly in a Rebel prison. He escapes, and joins up with the Army's spy service. McClellan has been disgraced and Pinkerton has returned to Chicago.. Lon and Margaret become reacquainted in New York City before the draft riots suddenly cost them dearly. Lon's black partner is killed, and Margaret leaves her husband, returning to Washington. Meanwhile, an enterprising young German-American actress plays the role of her life -- masquerading as a soldier to see the elephant. She is captured by rebels but saved by a Southern gentleman from rape. . . and worse. They also fall in love and are separated by the war. Throughout the tale lurks the dangerous presence of John Wilkes Booth and his outspoken hatred of Abe Lincoln, until the fateful night of April 14, 1865 . . . Even the newly formed Secret Service cannot protect the president from the assasin's bullet.