Donna Noble's life had changed ever since she last met the Doctor. She's realized that turning down the offer to join him on his travels may have been the worst decision she's ever made. Ever since, she's been investigating certain schemes and suspected alien activity in hopes that the Doctor is doing the same and that they'll reunite. Her investigation into Adipose Industries and their new weight loss pill turns out to be exactly what she's been looking for as the Doctor has been investigating Adipose as well. They join together to take down the mysterious Miss Foster who's weight loss pills are really turning the fat into little creatures called Adipose.