Alice O'Donnell

Alice O'Donnell was the systems technician onboard the Drum, an underwater mining facility in Scotland. She was a big fan of UNIT and the Doctor's work with them, and was thrilled when the Twelfth Doctor arrived.

When commanding officer Jonathan Moran was killed, her friend Cass took charge. She led the remaining crew to the base's Faraday cage, where they would be safe from the ghost leader Prentis.

When the Doctor decided to travel back to before the flood to uncover the mystery behind the ghosts, O'Donnell and Mason Bennett were the only ones able to get back to the TARDIS with him, and the two journeyed with him back in time. (TV: Under the Lake)