The Doctor and Donna Noble are both independently investigating Adipose Industries, a company that can make fat just "Walk Away" with a simple pill.  Things get more complicated when little fat creatures start popping out of people and, sometimes, consuming them whole.  The Doctor and Donna meet up while spying on the president of Adipose, Miss Foster.  The two team up in order to stop her from killing millions in her goal of raising children for an alien race.