Season 4

As with the preceding three seasons, Series 4 incorporated several ongoing story arcs which were resolved in the finale episodes. In Series 4 these threads included: Donna Noble’s evolution, Rose Tyler’s attempts to return to her original world and the Doctor, the disappearance of bees from planet Earth, recurring references to planets and moons disappearing, and the coming of “the Darkness”, mainly represented by the attempts of the Daleks and Davros to wipe out all reality. Additionally, most episodes include a running gag: namely, that people keep mistaking the Doctor and Donna for a couple.

1 Partners in Crime Russell T Davies James Strong Return of Donna Noble. First appearance of Rose Tyler since Doomsday.
2 The Fires of Pompeii James Moran Colin Teague Foretelling of the events in the final three episodes of Series 4; Peter Capaldi and Karen Gillan’s first character roles on the series.
3 Planet of the Ood Keith Temple Graeme Harper Reappearance of the Ood.
4 & 5
Pt. 1: The Sontaran Stratagem
Pt. 2: The Poison Sky
Helen Raynor Douglas Mackinnon Reintroduction of the Sontarans, return of Martha Jones. Second brief cameo of Rose Tyler.
6 The Doctor’s Daughter Stephen Greenhorn Alice Troughton Martha Jones leaves the TARDIS once again.
7 The Unicorn and the Wasp Gareth Roberts Graeme Harper Doctor Who’s take on Agatha Christie’s disappearance.
8 & 9
Pt. 1: Silence in the Library
Pt. 2: Forest of the Dead
Steven Moffat Euros Lyn Introduction of River Song. Subsequent death of River Song, though her soul is digitally preserved in the the Library.
10 Midnight Russell T Davies Alice Troughton Companion-lite episode; Catherine Tate’s role as Donna Noble is minimal. Third brief cameo of Rose Tyler.
11 Turn Left Russell T Davies Graeme Harper Return of the Bad Wolf meme and Rose Tyler. Doctor-lite episode.
12 & 13
Pt. 1: The Stolen Earth
Pt. 2: Journey’s End
Russell T Davies Graeme Harper Reintroduction of Davros. Return of Martha Jones, Jack Harkness, Sarah Jane Smith, Mickey Smith, and Jackie Tyler. First direct crossover with Torchwood and The Sarah Jane Adventures. Last regular appearances of Donna Noble and Wilfred Mott. Final appearance & death of Harriet Jones. Creation of Meta-Crisis Doctor.