Lena Korolev was the sister of Alexi Korolev.
When Lena and Alexi were children they were raised by their mother. Every year they went to a funfair. She also became friends with Pavel Fedorin. Eventually her mother fell ill with cancer, and on 30th November Lena decided to give her a merciful death, despite regretting it for years, promising to look after Alexi.
Eleven years later, Alexi joined the Somnus Foundation. She later tried to get into the Foundation, and was saved by Turlough and the Fifth Doctor. She was later attacked by a pack of birds controlled by the Foundation. When the Doctor took her back in time, she wanted to save her mother so that she could then save Alexi in the future. Turlough tried to stop her, but managed to persuade her by telling her how twisted time is. She wanted to do anything to get her brother back, even considering handping in the Doctor and Turloug, but the Doctor persuaded her otherwise, and after going to her childhood funfair,she admitted to switching off her mothers life support. After Pavel’s bunker was destroyed by a bomb, Pavel died in her arms. After Turlough was kidnapped, Lena and the Doctor headed to the Foundation. When the Foundation broadcast control over Moscow, Lena struggled against it, but eventually gave in. After the later communicated through the singularity, Lena’s mind met Alexi’s, who saw what happened to their mother, and forgave he, allowing them to return home. After the Somnus Foundation was destroyed, they promised the Doc they would live well, and look after Pavel’s grandmother.(AUDIO: Singularity)