An idealistic young girl arrives in Russia for an arranged marriage to the mercurial Emperor Peter. Hoping for love and sunshine, she finds instead a dangerous, depraved, backward world that she resolves to change.
1761, Catherine travels to Russia and marries the Emperor Peter. With hopes of marrying a great love, she soon realises Peter is a selfish brat who stands against everything she values. Feeling hopeless and suicidal, her servant presents her with an alternative path.
Catherine takes her first steps toward a coup. Taking advice from Marial, she attempts to seduce and recruit palace intellectual Count Orlo. After seeing Peter's brutal treatment of local nobles and unwillingness to listen, Orlo agrees to join Catherine's coup.
Catherine, Orlo and Marial continue their planning. They try to recruit an unhappy military general, Velementov, for their cause during palace celebrations honouring Peter's late father. Peter, noting Catherine's unhappiness at court, gifts Catherine a sterile lover.
Catherine tries to manage her reputation at court and her relationship with Leo, both of which distract her from the coup. Meanwhile, the influential Patriarch of the church dies, and a new one must be chosen. Orlo sees an opportunity to influence Peter in the decision.
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As the war with Sweden continues, Catherine and Aunt Elizabeth visit the military at the front. Grigor struggles with Peter and Georgina's liaison and poisons Peter to end it. When Peter falls ill, Velementov, Orlo and Marial all try to influence Catherine to takeover.
Peter has a new lease on life after his near-death experience. He is open to Catherine's progressive ideas of introducing art and science to court and wants to focus on an heir. Orlo tries to figure out who poisoned Peter and faces demons of his own.
Catherine feels optimistic about peaceful coexistence with Peter and their increasing chemistry. However, when smallpox breaks out in the servants' quarters, Peter reverts to his old ways. Meanwhile, Leo and Catherine's relationship suffers and Georgina misses Peter.
Catherine's political abilities are tested when she's given an opportunity to travel abroad with Peter and Velementov to discuss ending the war with Sweden. Velementov finally sees the potential of her leadership and decides to support the coup.
Tensions mount as Catherine and circle try to get regional counts on board with the coup. A few of the men end up killed. When a body is discovered later, Peter decides to torture everyone at the palace to find the murderous traitors. Catherine realises she is pregnant.
Catherine decides to move forward with the coup on her birthday. Peter isn't so easily overcome and holds Leo hostage as collateral. Marial betrays Catherine to Peter. Catherine realises the only chance for a greater Russia is to fight, without Leo. The battle begins.