A timeship was one of a number that were sent out to survey the Time Vortex and never returned, eventually being unearthed in the construction of a railway in 19th century England. Badly damaged, it hyper-evolved a nearby mole into a fearsome creature the size of a bear to protect itself.
The First Doctor found the timeship in the beast's cave and used it to shrink the beast to its normal size. He then set it to return to its owners, although the Doctor was unsure as to when it would arrive for them. He and Dodo Chaplet hurried away from the cave and departed in his TARDIS as the sound of another roared in the woods. (AUDIO: The Horror at Bletchington Station)