Voyage of the Damned
Rossiter was a Vinvocci attempting to regain the Immortality Gate.
Along with his partner, Addams, Rossiter infiltrated the staff of billionaire Joshua Naismith on Earth in order to salvage a piece of equipment referred to by Naismith as the Immortality Gate, and which the tycoon had recovered following the fall of Torchwood. Using a shimmer to disguise himself as human, he, along with the similarly disguised Addams, infiltrated Naismith’s inner circle. Their efforts to spirit the Gate away were disrupted by the arrival of the Tenth Doctor and Wilfred Mott. Rossiter and Addams were reluctantly recruited by The Doctor to stop The Master’s scheme to take over the Earth and facilitate the return of the Time Lords. Rossiter was one inch taller than The Master, but was able to disguise himself as one of the Master Race, and helped The Doctor escape The Master’s clutches. Then using Addams’ ship he, along with Wilf, destroyed several missiles aimed at them by The Master. When Addams dropped off The Doctor and Wilf at Naismith’s mansion for a final showdown with The Master, they presumably departed Earth. (The End of Time)
Rossiter was a panicky, skittish individual. After knocking out The Master, he declared that he had never hit anyone before, and when he and Wilf were manning the Hesperus’ asteroid lasers against The Master Race’s missile attack, he screamed and yelped throughout the attack. However, he also could be loyal and showed concern for The Doctor’s welfare when his partner began to pilot their ship away from Earth, saying, “What about The Doctor?” (The End of Time)