Donna Noble (Catherine Tate) regrets not taking up the Doctor’s (David Tennant) invitation to travel with him in the TARDIS. She has become an investigator to find information about him. The Doctor and she are both investigating Adipose Industries, which is selling a suspicious diet pill. The treatment uses latent body fat to create small white aliens called Adipose that leave human bodies in the night.

Exploring the company’s headquarters, the Doctor and Donna bump into each other. They are confronted by the alien Miss Foster (Sarah Lancashire) who is creating Adipose babies for the Adiposian First Family. She pursues them around the building and confronts them in an office. The Adipose, she explains, lost their breeding planet, and hired Miss Foster to find a replacement. The Doctor uses Miss Foster’s sonic pen and his sonic screwdriver to escape.

Miss Foster accelerates her plans. The Adipose multiply in London by the thousands. The Doctor and Donna try to prevent the human victims from dying. The Adiposian First Family arrive in a spaceship to collect their young. Despite the Doctor’s warning, Miss Foster is killed. The Doctor refuses to kill the baby Adipose and Donna remarks that Martha made him more human. She accepts his offer to travel with him and, getting ready to leave, she runs into Rose Tyler (Billie Piper) who disappears.

Reviews were positive. The Adipose special effects were impressive. Catherine Tate was much less crazy and irritating than she had been in The Runaway Bride, and eventually became a pretty great companion, in my opinion, holding her own with the Doctor. The news vendor Wilfred Mott (Bernard Cribbins) from Voyage of the Damned turns out to be her grandfather. The Adipose were unusual villains—disturbingly cute and surreal, like evil little Pillsbury doughboys. Viewers were thrilled with Rose’s surprise appearance.

Howard Attfield was supposed to play Donna Noble’s father, but he died, and the character of her grandfather was created. The theme to Hitchhiker’s Guide to the Galaxy pops up in the episode’s music. It was known that Rose would appear later in the season, but they somehow managed to keep her cameo in this episode a secret. Donna carried her luggage around in her car just in case she ran into the Doctor sometime. The Adipose ship resembles the spaceship at Devil’s Tower in Close Encounters of the Third Kind. Donna Noble and the Doctor work beautifully together as a comedy team.