Milady's ship is detained by a storm, and when she finally reaches England, Planchet has already warned de Winter of Milady's wicked plans; meanwhile, Planchet is now boarding a ship heading back to France. Therefore, when Milady's ship docks, she is received by an austere English officer who, with utmost politeness, escorts her to a castle some distance away and places her in a locked room. Milady is livid with anger and indignation, but after awhile, Lord de Winter appears. To her horror, she learns that she is a prisoner.
She tells her brother-in-law that her only reason for coming to England was to see him. De Winter is not fooled. He sarcastically acknowledges that her reason for coming is now fulfilled: she is a "guest" in his castle and they can visit together every day. Slyly, de Winter lets Milady know that he is aware of her first husband (Athos), as well as her recent plottings. And when he mentions her branded shoulder, she is ready to kill him — but he warns her not to try, for if she does, he will either kill her or send her to the public executioner.
De Winter then calls for his assistant, John Felton, and tells him to guard this wicked woman. He recounts many of the immoral and evil things she has done, and he warns Felton not to be deceived by her. Felton, who is deeply indebted to de Winter for many favors, promises to obey his master's instructions to the letter.
Meanwhile, back in France, the cardinal is wandering around the campgrounds, waiting for Milady's report. By accident, he encounters the four musketeers, who are reading a letter. Richelieu approaches them and engages in a rather guarded political conversation, during which Athos gets the better of the cardinal, who grudgingly leaves.
These chapters further reveal the dark and murky depths of Milady's vile nature. For example, other people might have committed some of her immoral acts for the sake of money, but we hear from de Winter that Milady is already wealthy. Milady's desire for de Winter's money is simply another aspect of her enormous greed and lust for power. De Winter finally concludes that her only reason for doing evil is for the sheer pleasure she receives when she is doing it. She can be compared to Shakespeare's Iago (in Othello); both Iago and Milady enjoy evil for the sake of evil.
Nonetheless, we should note that in spite of Milady's evil nature, she is treated politely and accommodatingly as a lady should be, rather than being thrown into a dungeon, where she belongs. This politeness is part of the nineteenth century's code of gentlemanly respect for womanhood — even though in this case, Milady's "womanhood" is indelibly corrupt and evil.
In Chapter 51, Athos is rather forward with the cardinal; he suggests that the letter he is reading is from his mistress, and he takes an even more dangerous chance when he says that the letter is not from either of two ladies who have been the cardinal's mistresses. The letter, of course, must be concealed at all costs because it contains the location of the secret whereabouts of Madame Bonacieux and the cardinal wants this information badly.