Born in 326 BC in Samothrace (present day Greece), Katherine was a foundling child. Raised by a loving family who taught her how to help others, she helped heal people with her knowledge of remedies, later becoming a healer for others as she grew older. In 292 BC, a volcanic eruption caused the death of many in her village, claiming her life as well. Following her first death and later revival, she met her teacher, Mantinea of Pylus, who taught her what she was, and how to survive.In 1270, in Northern England, she settled in a village where she met, Berta Symes, who was the village healer. Berta took her in and they became great friends. Even though Berta was the healer for the village, she learned a lot from Katherine. Berta believed that Katherine should be the healer, but Katherine told her that Berta gave love and care to people and that was a true healer. Katherine was happy and content in her role in the village, until the tax collectors demanded a large tithe.
An Immortal named Bartholomew was the head tax collector and priest, he manipulated the beliefs of the day, claiming the tax was God's will, but those who fought in the Crusade, would be wiped clean of sins.
Katherine, of course realized he was an Immortal and questioned his motives. Katherine later confronted Bartholomew and challenged him, but was shot in the back by his guard. When Katherine revived she found her village burned and the people slaughtered. She found Berta's necklace in the mud, and took it. She swore on it to hunt down Bartholomew.Over the centuries, Katherine tracked Bartholomew, who was still making money from other people's misfortunes though war and hunger. Katherine became a mercenary,and a gun for hire, helping people in need.
In 1993, while living in Chicago, Illinois. She met the love of her life, Nick Sutherland, who was a Chicago police officer. They met during an investigation of a serial killer. After they got married she revealed herself as an Immortal, and Nick accepted her explanation and assigned himself the role of voice of reason.
In 1998, Katherine and Nick rescued a girl from her kidnappers, and in payment, she request information on Bartholomew from her shady client, Mr Caruso. Katherine was eventually given the whereabouts of Bartholomew.
She explained her history with Bartholomew to Nick who became worried about her, but she insisted that she was all right.
Eventually, Katherine traveled to Paris to deal with Bartholomew. At his front company, "Mission for Children" head quarters building they met in the parking garage and face off when two of Bartholomew's goons show up with guns. Katherine was saved by Nick in a fast car. The couple discovered that Bartholomew was stealing money out of his charity and very few funds were ever actually received by any one but him.
The police, however, arrested Katherine and Nick for breaking and entering. An irate police officer told them that they were all ready investigating Bartholomew, and that they had managed to comprimise that investigation. The officer was set to escort Katherine and Nick to the airport, "to save them taxi fare," when he was killed by Bartholomew's goons.
Out of money and weapons, Katherine contacted Mr Caruso for assistance and his network provided guns and money. Katherine and Nick went directly to Bartholomew's home, and Nick dealt with the goons, while Katherine and Bartholomew finally meet in a challenge.Katherine took Bartholomew's head and received his Quickening. Katherine and Nick took the $30 million in diamonds Bartholomew had as his running money, and donated it to children's charities.
- Katherine was one of the candidates for the lead female character in Highlander: The Raven, but the role went to Amanda, portrayed by Elizabeth Gracen.
- Katherine once posed for the Kama Sutra.
- The actress Claudia Christian, who played Katherine, was a series regular cast member of the popular sci-fi TV series, Babylon 5, Tracy Scoggins, the actress who played Cassandra replaced Claudia when she left at the end of Season 4.
- The premise of Two of Hearts was twisted to accommodate the characters of Amanda and Nick Wolfe for the final Highlander: The Raven product. The lead male even retained the name of Nick, though as rating proved, it was an awkward fit.
- Two of Hearts is the only episode of Highlander: the Series in which not one regular cast member appeared in story.