Lena Korolev

 was the sister of Alexi Korolev. She tried to get into the Somnus Foundation. She was later attacked by a pack of birds. When the Fifth 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. (AUDIO: Singularity)