"The Conspirator" (PG-13, 121 minutes). Robert Redford's new film star Robin Wright, as the half-forgotten Mary Surratt, the first defendant tried after the assassination of Abraham Lincoln. John Wilkes Booth and his conspirators, including her son, held meetings in the Washington boarding house she ran. Was she a co-conspirator? James McAvoy co-stars as the young attorney required to argue her defense against his will (and his opinion she was guilty).