De Winter, suspecting that Felton is under Milady's influence, sends him on an errand away from the castle. That night, Milady hears a tap at the window; it is Felton. He has chartered a boat to take them to France, and he plans to file through the bars on her window and help her escape.
Felton is successful and helps Milady climb down a rope ladder. They board the boat and he tells her that he has to debark at Portsmouth in order to take his revenge on Buckingham before Buckingham leaves for France. Milady is convinced that Felton will be able to dispose of Buckingham; her vengeance will be fulfilled. It is agreed that she will wait for Felton until 10 o'clock before setting sail.
Felton's mind seethes with all of the horrible things he has heard about Buckingham. His strange, maniacal devotion to Milady, together with his fanatical religious notions, make him totally irrational. When he is allowed into Buckingham's office, he pleads for Milady's freedom, but Buckingham absolutely refuses. Crazed, Felton pulls out a dagger and stabs Buckingham. He tries to flee, but he is apprehended by de Winter.
As Buckingham is dying, he learns that Queen Anne's friend, Monsieur de La Porte, is outside; La Porte has a letter from the queen which he reads to the dying Buckingham, assuring Buckingham of Anne's love for him. After Buckingham dies, de Winter questions Felton, who maintains that he killed Buckingham only because of a matter concerning promotions. Then Felton sees the sloop with Milady on it sailing out to sea. Obviously she heard the cannon alerting the nation that something extraordinary had happened, and she surmised that Buckingham was dead. Instantly, she set sail — alone. Felton has been betrayed and abandoned.
These two chapters bring to an end the "English episodes" concerning Milady and the puritanical fanatic, Felton, whose religious blindness allowed him to become her dupe. Ironically, the cardinal casually remarked earlier: if all else fails, maybe some fanatic will rid the world of Buckingham. The cardinal was brilliantly prophetic. Dumas has arranged his material so carefully that neither author nor reader wishes to dwell upon the particulars of Felton's religious views; we are content to leave him to his destiny.