Many friendships and alliances flesh out the Mass Effect games' story, and some characters might see others as heroic protectors or even personal saviors. One such crew member, Miranda Lawson, was sure that she had made a true ideological ally in the Illusive Man. She later learned otherwise.
As of 2185, Miranda and the Illusive Man were two peas in a pod, fighting side-by-side to advocate Cerberus's message and look out for humanity in a large and scary galaxy. Miranda put her total trust in the Illusive Man, but over time, she realized what a mistake she had made. And in the rare instance Miranda makes a mistake, she is quick to fix it.
Those Who Appreciate Her Truly
Miranda was not born into an ordinary family. In fact, she had no mother at all; only a father, Henry Lawson, who used advanced science to modify his genome and create a pseudo-clone daughter, Miranda (there was also Oriana, whom Miranda rescued later). Miranda never had a good relationship with Henry; he was cold and demanding, showing no paternal warmth as he pushed his daughter hard to succeed and excel. Miranda deeply resented this household and fled as an adolescent, and she ended up approaching Cerberus, an organization that Henry had once supported. Miranda soon fostered a strong relationship with the Illusive Man, the head of Cerberus, because he recognized Miranda's talents and appreciated them. He was like a better version of Henry, in Miranda's eyes.
Like Henry Lawson, the Illusive Man wanted to advocate and protect humanity at any cost. Unlike Henry, the Illusive Man seemed to genuinely (even personally) admire, support and nurture his subordinates. The Illusive Man was almost like a foster father for Miranda, appreciating the depths of her skills and talents and putting them to good use. And unlike the overbearing Henry, who was self-absorbed and controlling, the Illusive Man gave Miranda a great deal of operational freedom and gave her everything she needed.
With this respectful relationship and a shared goal within Cerberus, Miranda worked closely with her boss and had rare, privileged access to him. This loyalty endured in 2185, when Miranda and the Illusive Man agreed that the Reapers were the true threat to humanity and that Saren's master plan was just the start. They were ready to face the endgame together, or so they thought.
Truth Vs. Deception
Miranda was ultimately loyal to the Illusive Man during her time aboard the SR-2 Normandy with Commander Shepard as they trekked across the galaxy to take on the deadly Collector race. Miranda stuck up for the Illusive Man despite Shepard's doubts, but that didn't last for long. The Illusive Man recklessly sought the truth of the Collectors and their power, and he put Shepard (and by extension, Miranda) in more and more danger to get what he wanted. He even sent Shepard's team into a trap aboard the Collector cruiser. When the time came to destroy the Collector base, the Illusive Man argued that it should be preserved and its secrets exploited for humanity. The Illusive Man had gone beyond defending humanity; he wanted to infuse it with the power of his enemies, regardless of the risks or ethical concerns involved.
This was too much for Miranda, who felt ideologically betrayed by her Cerberus boss and friend. She wanted humanity to be free of its enemies, not become those enemies, and she realized that the Illusive Man had been using her and Shepard ever since the SR-2 Normandy was launched. Miranda came to realize that Commander Shepard embodied the virtues of truth, honesty and courage, while the Illusive Man was rooted in lies, deception and exploitation. She had been lied to about the Illusive Man's true nature and goals, and that prompted her to officially break ties with her boss right before the Cerberus base was destroyed.
Miranda washed her hands of her boss and Cerberus as a whole, and she was ready to stand for truth and protection of humanity, like Shepard, while opposing the lies of the Illusive Man. Her old boss wanted domination of the galaxy, and Miranda refused to associate with such a maniac (the same was true of Jacob Taylor, the soldier who fled Cerberus). This was a blow to the Illusive Man, and he made up for it by choosing Kai Leng, the assassin, as his new #1 henchman. He had driven Miranda away with his lies and schemes, and he'd never get her back.