Donna tries to find the Doctor and that is the reason why she investigates strange happenings. This time she is on the trail of Miss Foster and her diet pills. She can't believe that the people who take the pills loose their fat over night. At the same time, the Doctor is investigating the same case and soon he and Donna are reunited. Together they find out that the diet pills create new babies for the Adipose race. When they try to stop Miss Foster, who is the nanny of the Adipose, she turns on her machine and the people on earth who have taken the diet pills loose their weight faster than they want to. Miss Foster is willing to kill thousands of people just to give live to new Adipose but the Doctor and Donna are able to stop her. Will Miss Foster get away with murder?
I have to say I really love this episode. It's so brilliant when you watch how the Doctor and Donna miss each other time after time and how happy they are both when they finally find each other. I love the scene where the Doctor and Donna are on different sides of the room and have to pantomime so they could understand each other. That's such a funny moment. This episode totally brings Donna back into the show and it's a bit like she was never really gone. There's a great chemistry between the Doctor and Donna because she is never really impressed of what he does and doesn't see him as a love interest like his other companions before. In this episode you have action packed but also funny moments and I think it's a great mixture for an episode. Another point is, that you just can't resist to love the Adipose because they are just so cute. A brilliant first episode for series 4.