Cassandra is an old flame of Michael's.She first appeared in Looking Glass.
Six years ago in Belarus, Michael was on an undercover mission, romancing with Cassandra. He later reveals his true identity to her and ask for her help to take down the Belarusian president Valerian Ovechkin, her husband. Cassandra helps Michael and Division and a replacement look-a-like takes over the spot as president.
Even though Michael does not appear to hold any romantic feelings for her, he does care for her deeply. She apparently reminds him of his previous wife and child. Cassandra's son, Max, is actually Michael's son even though she denies it. Nikita is aware of this fact and told Michael about it at the end of the "343 Walnut Lane " episode.
Cassandra has been identified as working for the MI6, and has been since the first operation started in Belarus.
In "Arising", Ari Tasarov assigned Cassandra to trick MI6 into thinking that Gogol had acquired aerial drone designs, promising that it'd be her last mission. What she didn't know was that Ari was planning on framing her team for the death of Sergei Semak. While one of her team began tailing the Gogol courier, Cassandra spotted Nikita on the street cameras and left to investigate. However, she was ambushed by Michael, who had just discovered her true allegiance. While Cassandra insisted that this would be her last mission, Michael deduced Ari's true plan and stopped it. But Ari in turn deduced that Cassandra betrayed him and leaked her identity to MI6, causing her to team to turn on her. After Nikita extracts Max before MI6 could use him as leverage, she then faked Cassandra's death. Micheal instructs Cassandra to "disappear" with Max and decides to stay out of contact with them for their sake.