Thomas Thomas was a young human boy in 1893 Yorkshire. He befriended Strax by offering the Sontaran driving instructions. Impressed, Strax allowed the boy to join him on the horse-drawn coach and continue to provide navigational assistance. Thereafter, he remained with Strax throughout a good portion of the operation to defeat Winifred Gillyflower. (TV: The Crimson Horror)
Behind the scenes
The name is an obvious pun on TomTom, a GPS service common in the United Kingdom at the time of the episode's premiere broadcast. The character is called "Urchin Boy" in the end credits, ostensibly to preserve the pun.