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.

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.

Four months after she launched a coup against her husband, a pregnant Catherine is gaining the upper hand in her war against Peter. The fact that he is deeply in love with Catherine and their unborn child does little to dissuade her from taking his throne.

Catherine, Orlo and Velementov begin their rule of Russia and unexpected obstacles appear. Peter is on a journey of self-improvement under house arrest but convinces Catherine to let him attend her coronation and hand over his crown.

Catherine's grief over the loss of Leo during the coup finally catches up with her. Peter's part in Leo's death, and the discovery that he just murdered a noble, causes Catherine to lock Peter in his apartments with only his mummified mother for company.

The Ottoman Ambassador pays Catherine a visit as tensions between the regions run high. Peter fights to win his allegiance and prove to the court he is more fun than Catherine, in an attempt to destabilise her by throwing a baby shower.

A crocodile roams the court, and Archie sends everyone into uproar by suggesting it might be an omen against Catherine's leadership.

Catherine is frustrated by the lack of meaningful change in her rule of Russia so far. Seeking to shake the court out of its complacency, she plays a joke on them involving a serf to prove a point, but it gets wildly out of hand with tragic consequences.

Catherine's team is falling apart and she begins doubting her reign when her mother comes to visit. She works hard to hide the realities of the court from her mother and puts on a science fair for which Russia must come up with the best invention.

Elizabeth pronounces that Catherine's baby will be born in five days and the court begins preparations involving rituals for Peter and Catherine. Conflict with the Ottomans heightens, and Catherine tries to run the country while on forced bed rest.

Catherine and Peter are co-parenting their newborn son, Paul, with the help of Elizabeth and trying to avoid their feelings for each other. When Paul goes missing, Peter and Catherine are driven together in their quest to find him.

Catherine makes a devastating discovery about Peter before traveling to the war front for a meeting with the Sultan. Peter considers his options now Catherine knows his secret and all parties come together for a final showdown at Marial's wedding.

Catherine and Peter seek some marriage guidance after the chaotic events of the previous day left them in an awkward place in their relationship.

Catherine is visited by the UK and US Ambassadors both wanting her to intervene in the War of Independence. Maxim takes issue with the public displays of affection between Grigor and Marial.

Catherine involves the peasants, nobles and merchants in a conference designed to bring change to Russia. Peter's hunt for revenge on an historic enemy threatens to destabilise Catherine's attempt to outlaw murder.

Arkady and Tatyana help Peter and Catherine through a rough patch as they clash over their son Paul. Catherine fears Paul will grow up to be a ruthless and careless leader and Archie and Elizabeth are alarmed when Catherine refuses to ordain him.

Peter is once again tormented by his father, Peter the Great's expectations and his failure to continue the legacy of his empire. Catherine must decide what to do about the unrest being stirred up in the regions, but Velementov is in no state to help her.

Catherine tries to persuade Peter to come home whilst Hugo redoubles his attempts to regain his kingdom. Georgina continues to play her complicated court games.

Catherine wants to bring more fun to the court. With Georgina's help she stages a festival of truth, jokes and stunningly clever ideas. Katya puts on a play that challenges Catherine's reign, and Catherine samples Peter's invention of salty desserts.

Catherine introduces divorce to the court with unforeseen consequences. Grigor befriends Maxim and goes stag hunting, and Elizabeth and Petrov go on a trip to the regions.

Under orders from Catherine, Grigor hides out in the forest with Paul. Catherine plays a dangerous game with herself to prove that her destiny lies in Russia, and grapples with the impact Peter's decisions have on her rule.

Catherine meets court scientist Nikolai, who announces a comet is about to pass through Russia. She uses this phenomenon to her advantage and in the face of some huge challenges, unearths a new side of her leadership.