On leaving Dumbarton, Sieur de Brézé was entrusted with the five-year old Mary until she would be handed over to the King of France. Also on board were James, John and Robert, three of Mary's father's illegitimate children, and her four Maries. Lords Erskine and Livingston, Mary's guardians were also of the party. After a turbulent journey during which all but Mary were seasick, especially Lady Fleming who, in vain, begged to be brought to shore, the fleet reached the port of Roscoff in Brittany. The King of France had ordered that Mary be made welcome and so she was. She continued the journey on horseback and boarded a barge at Nantes which took her up the Loire River through Anjou and Touraine. At Tours she was greeted by her grand-parents, Claude and Antoinette, the Duke and Duchess of Guise. Antoinette, who was not overly impressed by Mary's companions, immediately took over the education of her pretty grand-daughter.

Mary's first meeting with the royal nursery was to be at Carrières, where the Dauphin and his three-year old sister Elisabeth were staying with their governor and governess, the Maréchal and Madame d'Humières. If Mary hit it off at once with the young François, it was not the case with his mother, Catherine of Medici. Catherine showed up unceremoniously into the royal nursery and stood there watching the children. Mary took an instant dislike to her, as did most people and, unaware of who she was, asked her whether she knew that she was in the presence of the Queen of Scotland. Whereupon Catherine curtly asked whether she knew that she was in the presence of the Queen of France. This was a mistake which Catherine, jealous of Mary, would never forgive the child. Mary also made the acquaintance of her mother's brothers, the Cardinal of Lorraine Charles Guise and Francis Guise. Those were not her only uncles but they were the ones who would have the most dramatic influence over her. Ambitious and powerful, they plotted together to put their niece in a central position, and coveted the crowns of France and England through her. Charles was the dashing hero while Francis was cultured and brilliant but also sinister. A sensualist, he was popular with the ladies and is rumoured to have had an incestuous relationship with his niece. Mary certainly adored her uncle who undertook her education and to whom she always turned for advice. However, Francis would never have jeopardised the power of the Guise family by behaving inappropriately with her.

When she was eight years old, Mary received her first and last visit from her mother, Mary of Guise. She found her daughter metamorphosed into a cultured and refined French lady but all was not well at the French court. A man named Robert Stuart and purported to be an English spy was accused of attempting to poison Mary Stuart before her mother's departure. Although the man was hanged for it, the whole affair remained shrouded in mystery. As always when poison was involved, attention turned to Catherine. Catherine had however no reason to want rid of Mary at that stage.

Mary had another companion dear to her heart at the French court, Diane de Poitiers, the beautiful mistress of the French King. Catherine had resigned herself to this kind of ménage à trois but harboured a deep resentment for the woman who had everything she did not: beauty, breeding, taste and the King's heart. Henry's relationship with Diane was tantamount to marriage; she took care of the children, he wore her colours (black and white), entwined his initials with hers and spent most of his time with her. Henry had been only fourteen when his father decided to get the thirty-one year old widow Diane to "tutor" his dull and timid son. He fell in love with her from the very beginning and had no eyes for the Italian bride chosen for him, Catherine of Medici. When the young Catherine arrived at the French court, Diane and Henry were already lovers and it was in this humiliating state of affairs that she led her life. The daughter of a simple merchant and related to the Pope she was constantly reminded of how lucky she was to ascend to the French royal family. On the outside she appeared demure and eager to please but she was Machiavellian inside. The mysterious and sudden death of Henry's brother and heir to the throne was the first to be attributed to her. The French did not like this foreign unattractive woman whose only ally seemed to have been the French King, Francis I. To make matters worse, she was barren and her future as Dauphiness was uncertain. Finally, by the powers of the occult or not, Catherine bore a son, Francis. She bore a further nine children, Elizabeth, Claude, Louis, Charles, Edward-Alexander, Margaret, Hercule, and the twins Jeanne and Victoire. The twins and Louis did not survive. Edward-Alexander was known as Henry and became Henry III. Elizabeth was married to Philip II of Spain, Charles became Charles IX and Margaret became the notorious "Reine Margot". Catherine was now secure in her position and when Francis I died of the "French disease" (syphilis), the balance of power tipped in her favour.

At the time of Mary of Guise's departure, Diane fell ill and retired to her private château of Anet. The King, feeling miserable without her consoled himself by straying with Mary's Scottish governess, Lady Fleming. The King was usually faithful to Diane and the pretty but rather vacant Lady Fleming was but a pale imitation. Unfortunately, Lady Fleming fell pregnant and bragged about the King's indiscretion. Diane forgave and forgot but agreed with Catherine that Lady Fleming must be banished to Scotland. She returned in disgrace and gave birth to who became known as the "Bastard of Angoulême". For Mary, the loss of Lady Fleming was bitterly felt when Catherine replaced her with her own woman, the sly Madame de Paroys.

Nevertheless, Mary's golden childhood continued; poets such as Ronsard and Du Bellay sang her praises, and Charles although eight years younger, developed a fascination for her tainted by the early signs of his madness. Francis was weak and relied on her constantly, Margaret or Margot was wild and precocious, and Edward-Alexander or Henry was effeminate and his mother's favourite. Mary's Guise uncles watched the sickly boy Francis with great interest, and constantly pressed the King for a marriage between Francis and Mary. In their minds, it would not be long before he died and Mary became Queen of France. Catherine saw little to gain from such a union which would place even more power in the hands of the Guise family. Francis was still only fourteen and his affection for Mary was but of a brotherly kind. However, the Cardinal of Lorraine pointed out that uniting Scotland to France would strengthen the latter against its usual enemy, England. Furthermore, the protestant John Knox and Mary of Guise's half-brother James Stuart were stirring Scotland up against the Church of Rome, a situation which the King of France could not allow to continue. Thus Henry I gave his consent and the public marriage document was signed on 19th April 1558. On the 4th of that month, Mary, guided by her cunning uncles, had also put her signature to three secret and controversial other documents. In those, she agreed to hand over Scotland to France should she die without an heir, to assign the revenues of Scotland to the King of France until he had recovered the money spent in defending that country and in the last, she renounced any agreement which contradicted the two declarations. A lavish marriage ceremony took place in the Cathedral of Notre Dame, followed by huge rejoicings at which Scottish commissioners were present. However, the poison issue was once again raised when nine of them were later taken ill and four died. The couple then retired to the château of Villers-Cotterets but the honeymoon was a brief one. The Cardinal, impatient to see the marriage consummated, paid them a visit followed by the King himself who decided that Francis should join the camp at Amiens for the benefit of his health.

In November 1558, Mary Tudor of England died and was succeeded by Elizabeth, her half-sister. The Guise brothers, always keen to turn any situation to their advantage, proclaimed that Elizabeth was illegitimate as her mother's marriage to Henry VIII was invalid. The King of France would not go to war with England over this issue but agreed that Mary, as sole legitimate heir, should now cross the Arms of France and Scotland with those of England. This was another fatal mistake for which Elizabeth would hold Mary personally responsible for the rest of her life.

The year 1559 opened up a series of royal marriage celebrations. Claude was married to the Duke of Lorraine, Elizabeth was married to Philip of Spain by proxy in June, and Margaret the King's sister, was affianced to the Duke of Lorraine. On 30th June however was sparked off a chain of events which were to mark the end of Mary's golden days. Catherine, who is said to have possessed extra-sensory perception, received a prophecy from her astrologer Nostradamus, that the King would die wounded. He had had a recurring dream in which a young lion fought with an older one and gouged his eye out, and the King's escutcheon was engraved with a lion. At the double wedding celebrations, Henry who was a keen jouster, challenged several partners, including the Count of Montgomery, a young man from Normandy of Scottish descent. When Henry, who was showing signs of fatigue, challenged him a second time, Montgomery and Catherine both begged that he be excused. Henry would have none of it and ordered Montgomery to joust again. And so the premonition came true; Montgomery accidentally struck the King's helmet and a splinter entered his eye. Henry fell to the ground, blood pouring from his wound. He was taken to the Hôtel des Tournelles where he died ten days later. Montgomery, a protestant, was of course suspected but Henry had insisted that he should not be blamed for the accident. Catherine showed genuine grief at the loss of this husband who had never loved her, and adopted the motto "Lachrymae hinc, hinc dolor" (Hence the tears, hence the pain). But the long-suffering wife was now in a position to dish out her first revenge against the rival who had usurped her place in the King's heart, Diane. Catherine banished her to Anet and demanded the return of all the expensive gifts Henry had bestowed upon her, including the beautiful castle of Chenonceau. In exchange, Diane was given Chaumont which Catherine believed to be an unlucky castle.

Francis succeeded his father and Mary became Queen of France and Scotland and Queen of England by name. The carefree days were over. Catherine showed her all the reverence that was due to her but she was only biding her time. Soon, Francis would make way for her next son, Charles who she could mould at leisure. Francis was no more than a frightened little child who clung to Mary for comfort. The Guise brothers were jubilant. The union of the two crowns meant that they were now in power both of the army and the State; Francis could be bullied into virility they believed and beget a child. The Cardinal became one of the most hated men in France. He started the persecution of the protestant Huguenots and may have suggested to Mary that she get herself pregnant by a lover. Mary was beginning to be aware of the devious, scheming and ambitious men and women who surrounded her. Her health was giving some concern as she was prone to fainting fits and mysterious pains, perhaps caused by indigestion. At Amboise, she and Francis were subjected to a terrible scene. A plot to kidnap the King and the Queen and to put the Huguenot King of Navarre on the throne had been uncovered. The Guise brothers decided to take this opportunity to show all what became of those who opposed their power over the King. Mary and Francis were made to watch the torture and mutilation of the culprits from the balcony of Amboise castle. Catherine and the Guise brothers also looked on unmoved but Mary, who abhorred violence as much as the King did, rose to leave the balcony. Francis, uncharacteristically ordered her uncles to step aside to let their King and Queen pass.

Then, in June 1560 James Hepburn Earl of Bothwell, the man who would later become Mary's third husband, brought her the sad news of the death of her beloved mother in Scotland following a long illness. Mary was grief-stricken while her husband's own health continued to deteriorate. Rumours of strange wasting diseases which gave the King a craving for babies' blood began to spread. Francis did not cope well with his people's hatred for him and leaned on Mary even more. He developed an abscess in the ear which steadily worsened. As the court prepared to leave Orléans for Chenonceau, Francis fell off his horse and had to be put back to bed. Mary sent for Ambroise Paré, a Huguenot and reputed to be the best surgeon in France. Paré told Mary that the abscess was a tumour which would reach the King's brain if not removed. But Catherine of Medici, no doubt motivated by her own aspirations for Charles and herself, delayed the operation until it was too late. Francis died on 5th December 1560. With the loss of her husband, Mary also lost her status of Queen of France. She retired for the customary forty days of mourning in a dark chamber. Charles was the new King and Catherine pushed the Guise brothers out of their position. But the Guises were not the type to give in without a fight. To them there was only one solution: Mary must marry the new King, sane or not and produce a child. As an alternative they suggested her sister-in-law's step-son, the deformed and mentally imbalanced Don Carlos of Spain. Mary shrank from the prospect.

Mary received a few more visits. One from her cousin Henry Stuart, Lord Darnley, who would become her second husband, sent by his ambitious mother to offer her condolences, but more likely to introduce her son to the young widow. At Fontainebleau, Mary was sought out by the English Ambassador, Sir Nicholas Throckmorton, who demanded the ratification of the Treaty of Edinburgh. Mary, continuing in the spirit and the belief which had been instilled into her by her uncles and father-in-law, flatly refused to ratify the Treaty. Elizabeth I of England never forgave her this insolence. Mary then moved on to the Abbey of St-Pierre-Les-Dames in Rheims where her aunt Renée of Guise presided over as Abbess. On her way, she met her half-brother James Stuart who pressed her to return to Scotland, and filled her in on the conflict raging there between Catholics and Protestants. In the meantime, Catherine had managed to fail the marriage plans of the Guise. She would not allow Mary to marry Charles and she had offered Philip of Spain the hand of her daughter Margaret for his son Don Carlos. Philip viewed this alliance as far more favourable to him and accepted. Cast in the shadow of her vengeful mother-in-law there was little left for Mary to do except prepare to return to and rule over her Scottish realm. She delayed her departure as long as she could but finally sent for Bothwell to act as admiral of her fleet. Broken-hearted and full of dread she set off from Calais harbour on 14th August 1561. Catherine of Medici had won.