Addams

Addams was captain of a Vinvocci salvage team who had come to Earth to retrieve the Immortality Gate, a Vinvocci medical device that could rewrite the medical templates of entire planets.

Biography
Addams and her partner Rossiter discovered the billionaire Joshua Naismith had acquired the Gate to make his daughter immortal. Addams and Rossiter used shimmers to disguise themselves as human technicians. They set about repairing the Gate, hoping to take it back to their ship. Addams found the shimmer uncomfortable, and deactivated it whenever she could.

Their progress was too slow for Naismith, who sought an expert who could fix the Gate more quickly. He had the newly resurrected Time Lord,, captured and brought to the mansion. While Rossiter worried another non-human would blow their cover, Addams believed this expert might prove useful in fulfilling their mission. Addams watched from her makeshift laboratory in the basement as the Master quickly repaired the Gate.

The Tenth Doctor and Wilfred Mott infiltrated Naismith's mansion and discovered Addams, but the Doctor immediately saw through her disguise and deactivated her shimmer with his sonic screwdriver. Addams and Rossiter explained the purpose of the Immortality Gate to the Doctor.

As the Master used the Gate to transfer his personal genetic template over the entire human population, Addams and Rossiter watched, helpless, from their basement laboratory as the readings from the Gate went haywire. She escaped with Rossiter, the Doctor and Wilf to her ship in orbit around the Earth. As captain, Addams decided to evacuate the area, but the Doctor used his sonic screwdriver to disable the ship.

When the Doctor used the ship to return to the Naismith mansion, Addams worked navigation while Wilf and Rossiter warded off the Master's missiles from laser pods. The Doctor leapt from the ship's hatch as it sailed over the mansion, and Addams dropped Wilf off before presumably leaving with Rossiter. (TV: The End of Time)

Personality
Addams was calmer than Rossiter, and was good at making decisions under stress. However, she sought to avoid trouble wherever possible, and was reluctant to help the human race. This put her into conflict with the Doctor, whom she angrily labelled an idiot. (TV: The End of Time)

Behind the scenes
Russell T Davies wrote in The Writer's Tale that he had written Addams as Sinead Keenan, who is an inspiration to him.

"The whole point is to find actors like David and Bernard, actors who can do anything, actors who, literally, inspire me. They make writing challenging, and brave, and wonderful. Put those two in a room, and I think I can write anything. Anything. Which feels brilliant. Oh, and Addams, too. I know she hardly matters, but she's important to me. I love Addams. There is something so vivid and right about her. I absolutely love that woman, Sinead Keenan, who plays Russell Tovey's girlfriend, Nina, in Being Human. I think she's a stunning talent, and I found myself writing Addams as her. It's not often I do that, write for a specific actor, but she's an inspiration. She's so good. And lo and behold, she's free, so we've cast her."

- (Russell T Davies - The Writer's Tale)