Tim Lunn

Tim Lunn was Cass's sign language interpreter aboard the Drum, an underwater mining facility in Scotland. He also had a crush on her but was too nervous to admit it.

When their commanding officer Jonathan Moran was killed and transformed into a ghost by Prentis, Cass took charge and led the crew to the base's Faraday cage. When the Doctor arrived, he hatched a plan to trap the ghosts that involved Lunn leading them to Mason Bennett. However, instead of staying together, the ghost of Richard Pritchard continued to follow Lunn. The ghost picked up a wrench, ready to finish Lunn off, but went away at the last moment.

When the Doctor decided to go back in time before the flood to figure out the mystery of the ghosts, Lunn became trapped with Cass and Clara behind one of the flood doors. (TV: Under the Lake)