As soon as Mary I took the throne, Simon Renaud, the Spanish ambassador to England, immediately engineered a marriage between Mary and the Crown Prince of Spain, Philip II, allying the two countries. Although mostly quite merciful to her enemies and conspirators against her, Mary treated her religious opponents with ruthlessness. Her marriage to a Spanish prince only reinforced her religious fanaticism. Although Elizabeth remained Protestant, Mary started working hard to restore Catholicism in England.
Although Elizabeth was next in line in the succession, Mary placed two other relatives above Elizabeth in her court, citing Elizabeth's illegitimate birth as her reason. Of course, this greatly insulted the princess. Although she remained fairly loyal despite her anger, many people in England encouraged her to conspire against her increasingly unpopular sister. In 1554, Sir Thomas Wyatt the Younger's Rebellion rose and failed. Enraged, Mary threw the traitors in the Tower of London and quickly asked Elizabeth to come to London from one of the royal country homes where she was staying. Elizabeth pretended to be sick and asked for doctors to come see her, thus wisely avoiding the London scene, where heads were soon rolling. Calling Elizabeth's bluff, Mary then decided to send doctors to see if Elizabeth was truly too sick to come. The doctors brought Elizabeth to London. On the way, she made sure to let everyone on the streets of London see her, in order to her increase her public presence and popularity. Elizabeth desperately alleged that she was not involved with Wyatt, but Mary refused to listen to her sister, or even read her letters, and sent her straight to the Tower of London.
On April 11, 1554, Thomas Wyatt was executed. But Elizabeth was so clearly popular with the people that Mary decided to move her to a more comfortable location, although she still would be kept under close watch. She was sent to the pleasant but out-of-the-way house at Oxfordshire. On the way there, as Elizabeth passed through various towns, the people cheered, cannons were fired, and church bells rang. Despite her constant letters to her sister, Mary repeatedly denied her release.
Soon, Mary announced that she was pregnant. However, the symptoms she had taken for signs of pregnancy in fact were the indications of an ovarian disease. Mary wanted to give the crown to her husband Philip, but Parliament refused. Thus as Mary was dying Philip met with Elizabeth, trying to convince her to marry him so he would remain a ruler of England. Of course, Elizabeth refused. Philip went home, but would return in 1557 with a proposal to marry Elizabeth to one of his Hapsburg cousins.
On November 17, 1558, Mary I died. Nobility filled the road to Elizabeth's country home, hoping to reach Elizabeth early and make a good impression on the new sovereign. Now 25 years old, Elizabeth ascended the throne of England. Trying to consolidate her power, Elizabeth did what she could to minimize the Catholic-Protestant conflict in the country with passage of a religious settlement act in 1559 that, despite making Protestantism the legal religion and Catholicism officially illegal, was actually very tolerant. Nonetheless, the Catholic world saw her as an enemy, and in 1570, Pope Pius V announced an interdict against Elizabeth that encouraged English Catholics to revolt against her.
Renaud was a very perceptive diplomat, and from the start he saw how much the people loved Elizabeth, who reminded them of Henry VIII much more than did Mary. Mary's marriage to Philip II of Spain angered most of England. Mary was hated for her routine burning of Protestants, and a popular rhyme of the day went: "When these with violence were burned to death, / We wished for our Elizabeth." Furthermore, when the Catholic monarchs of England proclaimed that Elizabeth was an illegitimate bastard, this only angered the people more. Some people suggested that Elizabeth marry a man of the Plantagenet line named Courtenay, hoping that this union of the Tudors and Plantagenets would prove able to topple Mary's Catholic government. But Elizabeth, who had seen enough members of her family lose their heads already, was cautious and unwilling to commit treason. Instead, she preferred to wait patiently for her succession. Nevertheless, the possibility that Elizabeth might cooperate with the Courtenay plot greatly frightened Mary, who felt increasingly threatened by her half- sister.