Mason Bennett

Mason Bennett was the marine geologist onboard the Drum, an underwater mining facility in Scotland.

When commanding officer Jonathan Moran was killed, his 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 Twelfth Doctor decided to travel back to before the flood to uncover the mystery behind the ghosts, Bennett and Alice O'Donnell 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)