"Partners in Crime" is the first story of Series 4 of the revival Doctor Who. It stars David Tennant as the Tenth Doctor, Catherine Tate as Donna Noble, and features Bernard Cribbins as Wilfred Mott. Catherine Tate had been a companion for a previous Christmas special, The Runaway Bride, but this episode reintroduces her as the regular companion for Series 4.
Sometime after the events of Voyage of the Damned, The Doctor has returned to earth to investigate a company that has a miracle weight loss pill. Donna Noble, who had previously been a somewhat vapid woman, has been inspired by her previous meeting with The Doctor to investigate the world more, and is doing her own freelance investigation of the company. In the first few scenes of the episode, The Doctor and Donna Noble are only a few dozen feet away from each other, but humorously avoid meeting each other. Soon, however, as the fat pills are revealed to be an alien plot to create alien babies through parthenogenesis out of people's fat, the Doctor and Donna bump into each other, are captured, escape, run around a lot, and finally the alien menace of the week disappears.
The episode is mostly used to introduce Donna Noble and set up her relationship with the Doctor. The aliens, cute little Pillsbury Doughboy type creatures called "The Adipose", are rather cute and silly, and are not really the focus of the episode. The focus of the episode is on the chemistry between Donna and The Doctor, which is both warm and humorous (especially in a scene where Donna mines her story to the Doctor through two windows).
As I have mentioned before, Doctor Who can be both mind-bending science-fiction show and silly camp, and often both at the same time. This episode is incredibly fast-paced, entertaining camp, built for general amusement, but it also succeeds beautifully. "Partners in Crime" is a very good opening for what would turn out to be a very good series.