Beth Summers was a 12-year-old human girl from the 21st century who helped the Tenth Doctor escape from a temporal trap in Victorian England.
When staying at her grandmother's house in the days leading up to Christmas 2009, Beth found an advent calendar from the mid-1800s that contained photographs of her family from that time. When she opened a window on the calendar that was still closed, she was transported back in time to 1859.
Whilst there, she met the Doctor and together they discovered that an unknown alien had trapped them both inside the house while he attacked the TARDIS outside. Beth helped defeat the alien by taking a photograph of him, trapping him in the temporal prison and freeing her and the Doctor. (PROSE: The Advent of Fear)