Everyone knows the story of Abraham Lincoln’s assassination in 1865, but few are aware of the original conspiracy to kill him four years earlier in 1861, literally on his way to Washington, D.C., for his first inauguration.

The conspirators were part of a white supremacist secret society that didn’t want an abolitionist in the White House. They planned an elaborate scheme to assassinate the President-elect in Baltimore as Lincoln’s inauguration train passed through, en route to the nation’s capital. The plot was investigated by famed detective Allan Pinkerton, who infiltrated the group with undercover agents, including Kate Warne, one of the first female private detectives in America.

Had the assassination succeeded, there would have been no Lincoln Presidency and the course of the Civil War and American history would have forever been altered.