Martha Jones summons the Doctor back to UNIT and modern-day Earth, but an old enemy lies in wait.
“The Sontaran Stratagem” features the first appearance of the alien Sontarans to the series since the 1985 Colin Baker story The Two Doctors, as well as former companion Martha Jones (Freema Agyeman), last seen in “Last of the Time Lords”. The episode takes place on present-day Earth, where Martha and UNIT summon the Doctor (David Tennant) for assistance concerning ATMOS (Atmospheric Omission System), a revolutionary piece of green technology installed in 400 million cars worldwide. ATMOS is later revealed to be part of a Sontaran plot to poison the atmosphere.
Show runner Russell T. Davies had considered making the Sontarans return since the revival of the series and wanted to show changes in Martha’s personality after her departure. Critics gave generally positive reviews, praising the return of the Sontarans, Christopher Ryan’s portrayal as Staal, and Raynor’s writing; some stated Raynor improved from her previous episodes.