[s4e1] Partners In Crime 【Verified Source】

" Partners in Crime " is the premiere episode of Season 4, first broadcast on April 5, 2008. It serves as a comedic and lighthearted reintroduction of Donna Noble (played by Catherine Tate) as a full-time companion to the Tenth Doctor (David Tennant). Plot Summary

The story follows the Doctor and Donna as they independently investigate , a company marketing a revolutionary "miracle" diet pill in London. The company’s slogan, "the fat just walks away," turns out to be literal: the pills transform human body fat into small, white, marshmallow-like aliens called Adipose . Doctor Who season 4 episode 1 review: 'Partners In Crime'