At dawn on the 24th of February, 1895, a bomb exploded in the Houses of Parliament. The security forces reacted immediately and arrested Michael Chapman, a young worker linked to anarchist groups, near the place of the attack. Mycroft Holmes is in charge of investigating the explosion for the Crown prosecution and needs to determine if the attack is the action of a lone wolf or part of a bigger plot.
It appears to be another easy case when he discovers that the detective hired by Michael's parents to prove the young man's innocence is no less than his brother Sherlock Holmes. The duel between the two most brilliant minds in London begins. Is Chapman an unfortunate young man that fell in the wrong company or a member of an anarchist cell?