Not until about 20 minutes into The Conspirator do you realize why Robert Redford would direct a historical drama about the trial of one of the conspirators behind Abraham Lincoln's assassination.
The opening act is a well-crafted recounting of the conspiracy to simultaneously murder Secretary of State William Seward and Vice President Andrew Johnson, culminating with John Wilkes Booth gunning down Lincoln inside Ford's Theatre. Redford's impressive attention to detail, here and throughout the film, includes the wooden brace Booth used to jam the door leading to Lincoln's theater box, the diagonal placement of Lincoln on the bed inside William Peterson's boarding house because the president was too tall to lie straight, and Secretary of War Edwin Stanton (Kevin Kline) ordering a hysterical Mary Lincoln out of the room.
As Booth and his cohorts are rounded up, the government eventually beats a path to a boarding house run by Mary Surratt (Robin Wright), where the assassination plot was allegedly hatched. Under orders from Seward, Surratt is tried before a military tribunal where she is not allowed to testify in her own defense, and neither she nor her attorney, Frederick Aiken (James McAvoy), are privy to the prosecution's evidence prior to trial.
It's only when the story line shifts focuses onto this Gitmo-style simulacrum, with Seward playing the part of a 19th-century version of Cheney or Rumsfeld, that Redford's motives become far clearer than those of his characters. Aiken, a former Union soldier, is cast as a war hero and an idealist, but the only adversity he suffers for his unpopular defense of Surratt is banishment from his gentlemen's club and the occasional anxiety of his fiancée.
Meanwhile, we're left puzzling over Mary's relationship with her son John (Johnny Simmons) and daughter Anna (Evan Rachel Wood), both of whom are strangely reluctant to come to their mother's aid. And other questions will come to irritable viewers, too, like why does every Southern character speak with such a clichéd drawl? (Tom Wilkinson's senator from Maryland sounds as if he were voice-coached by Foghorn Leghorn.)
As some evidence of Mary's culpability gradually emerges, writer James Solomon waffles between defending Mary's innocence and indicting the legal apparatus erected to prosecute her. The latter is a more bloodless endeavor, but make no mistake: There was unfairness here that deserves contempt regardless of Mary's guilt, including the improper influence exerted to ensure a death sentence. The trial and hanging of Mary Surratt is an important, nearly forgotten episode of American jurisprudence. However, The Conspirator is so captivated by its historical heft that it forgets to engage its audience in the figures at the center of the diorama.