Documentary filmmaker Errol Morris investigates the case of a man who became an authority on capital punishment, but was discredited when he got involved on the wrong side of a court case. Leuchter, a meek man whose appearance belies his grim expertise, develops what he says is a more effective electric chair. Before long he's in demand from officials who want his opinions on other kinds of execution. But when called to aid the case of an accused Holocaust denier, Leuchter's problems begin.