Her next famous undertaking, which involved the lives of various persons of high rank, was the scheme to persuade Monsieur the Dauphin to refuse to marry Mlle. de Montpensier; Queen Anne was opposed to this union, and Mme. de Chevreuse gained to their cause a number of influential friends who were all madly in love with her. The ever vigilant Richelieu having discovered the plot, Monsieur confessed. In this conspiracy, M. de Chalais lost his head, other plotters lost their positions, and some were exiled. Mme. de Chevreuse was forced to retire to Lorraine; there she set in movement a vast plan against Richelieu and France, allying England and various princes, but, by the arrest of Montaigu, the plot was discovered, the alliance broken up, and peace restored.
In 1626, by request of England, Mme. de Chevreuse returned to France. For a time she was quiet and seemed to favor Richelieu, but she soon captivated one of his ministers, the Marquis of Châteauneuf. Richelieu discovered the latter's weakness, and, having captured his correspondence, sent him to prison, where he remained for ten years. The fair intriguer was exiled to Dampierre, the cardinal fearing to send her out of France on account of her influence with the Duke of Lorraine. She managed to steal into Paris at night and see the queen; when discovered, she was sent to Touraine where she began the dangerous task of carrying on the correspondence between the Dukes of Savoy and Lorraine and England, and between Spain and Queen Anne. Even when this correspondence was intercepted and the queen confessed all, Richelieu was afraid to banish Mme. de Chevreuse; though he believed her to be at the bottom of all the current intrigues, he knew that out of France she would stir up the rulers of England and Spain as well as the Duke of Lorraine and others hostile to the cardinal.
Violence being out of the question, because of her influence in England and of the prominence of her family, he decided to win her over by kindness; he even sent her money, but she was too shrewd to permit Richelieu to outwit her, always paying him back in his own coin. However, that kind of play was too dangerous for her and she escaped to Spain. As soon as her departure became known, Richelieu set to work every means in his power to bring her back, sending her an urgent invitation to return and promising to pardon her past. When his messages reached her, she was already in Madrid, where she was royally received as the friend of the king's sister, Anne; there, by means of her beauty and wonderful intelligence, she conquered every cavalier. When the war broke out between France and Spain, she left for England where she was welcomed like a visiting queen.
Richelieu, anxious for the support of the Duke of Lorraine in his war against Spain and Austria, needed the coöperation of Mme. de Chevreuse, and with that end in view sent ambassadors to London to arrange for her return; but an agreement was not an easy matter between two such astute politicians, and negotiations went on unsuccessfully for over a year. Her subtleness, apparent docility and invincible precautions were pitted against the artifices and dissimulation of the cardinal; both employed all the astute manœuvres of diplomacy and exhausted the resources of consummate skill in gaining the point desired by each. The cardinal failed to convince her of her safety.
Mme. de Chevreuse soon formed about her a circle of émigrés—Marie de' Medici, Duc La Vallette, Soubèse, La Vieuville, and many others. This coterie was in open correspondence with Spain, Austria, and the Duke of Lorraine. From every side, Richelieu felt the intriguing hand and influence of Mme. de Chevreuse, and decided to put forth another effort to get her to return, this time sending her husband; but not sure of the latter's sincerity and in fear of him, the duchess concluded to leave England for Flanders, and, escorted by a squad of dukes and lords, departed like a queen.
At Brussels, she entered into open relations with Spain, drawing over the Duke of Lorraine. She was accused of being in the plot of Cinq-Mars and the Duke of Bouillon with Spain; when Richelieu exposed this to Queen Anne, the latter for the first time became her enemy. Just at this time of his triumph, Richelieu died, his death being followed soon after by that of Louis XIII., who left a special order for the exile forever of Mme. de Chevreuse, whom he called Le Diable. The queen-regent, however, recalled her, and set at liberty her friend, Châteauneuf, who had been imprisoned for ten years.
When Mme. de Chevreuse returned to Paris after an absence of ten years, her beauty was still unimpaired, she possessed an experience such as no man of the day could boast, was personally acquainted with nearly every great statesman and aware of the weak points in every court of Europe. While she could now count on the support of the majority of the princes, plots were being formed about the queen-regent, the object of which was to persuade the latter to give up the friends who had served her faithfully for so many years. La Rochefoucauld was sent to meet Mme. de Chevreuse and to inform her of the change of attitude of the queen-regent; as her devoted friend, he advised her to abandon, for the present, all hopes of governing the queen and to devote herself entirely to regaining her favor and to preparing for the possible fall of Mazarin.
After securing the release of her friend Châteauneuf, Mme. de Chevreuse set to work to restore him to his former office of Guard of the Seals, but did not succeed. She then turned her attention to undermining the power of Mazarin, agitating all émigrés returning to France and starting the most outspoken denunciation of the policy of the cardinal, his injustice and tyranny against the nobility. The cries of disapproval became so general that Mazarin was kept busy warding off the blows aimed at him by his enemy; the latter succeeded in placing Châteauneuf as Chancelier des ordres du roi and in having his estates restored to him, while Alexandre de Campion she placed in the household of the queen. Mazarin, living in constant dread of her, managed to thwart two of her cherished schemes—the restoration to the Duke of Vendôme of the government of Brittany and the placing of Châteauneuf in the ministry—upon the success of which depended her own influence and power.
Finding that ruse, flattery, insinuation, and ordinary court intrigues were of no avail, she turned to other methods. The Importants, a party made up of adventurers and a large number of the nobility, were making themselves felt more and more; they were opposed to Richelieu and Mazarin, and Mme. de Chevreuse became their chief and instigator. Failing to succeed with the cardinal's own methods, she decided to assassinate him, but the plot was discovered, the Duke of Beaufort was arrested and all the princes of the party of the Importants were ordered to leave Paris. Mme. de Chevreuse was compelled to depart from court and retire to Dampierre, and then to Touraine, where she did everything in her power to assist the friends who had compromised themselves for her. During her first exile she had had the consolation of the friendship of the queen; but now she was banished by the very friend whom she had served so well and who had up to this time been able and willing to afford her comfort and protection. Through Lord Goring, Count Craft, and the Commander de Jars, she opened up correspondence and negotiations with England, but was again surprised by the vigilant Mazarin and sent to Angoulême; determining to escape, after many hardships, she successfully reached Liège; from there, as head of all foreign intrigues against France, she continued to thwart Mazarin's foreign policy.