When the Ninth Doctor learnt from Charlotte Cobb that her husband Peter Cobb had mysteriously died after being followed by Lend-a-Hand girls, Rose went to Lend-a-Hand House and found that humans were also being converted into Lend-a-Hand girls. Travelling to Lend-a-Hand House, the Doctor discovered the Kustollon Igrix had travelled back in time, and planned to use Lend-a-Hand girls, initially made up of female humans, but later including biotechnology grown from Kustollon genestuff, to alter history so that humanity would be given whatever they desire and never venture out into space, and consequently never win a battle between Earth and Kustollia in 3046.
To do this, Igrix killed scientists who would create things "that would make people unhappy". Igrix' first major step was to destroy the Moon in 1966, preventing any staging post from which to break out into space. With the help of Peter's work on DNA resequencing, the Doctor created a virus containing genetic instructions from Rose in the form of perfume, which Rose threw at the Lend-a-Hand girls, making them humans with human instructions.(COMIC: The Love Invasion)