A call from Martha brings the TARDIS back to Earth, just in time for Donna and the Doctor to witness a UNIT raid on the Atmos factory. Standard-issue in more than half the automobiles in the world, Atmos cancels out all harmful pollution emissions from any car – and the Doctor recognizes it as something far ahead of current human technology. But as everyone knows, Atmos is the invention of former teen prodigy Luke Rattigan, who now heads his own academy for developing young genius. A visit to Rattigan’s academy reveals that he is in league with a Sontaran invasion force, a discovery from which the Doctor barely escapes alive. He decides to dissect an Atmos device for himself, only to accidentally trigger a weapon within it that emits toxic gas. Using a clone of Martha to keep UNIT’s attention away from the real danger, the Sontarans activate all of the gas emitters in all of the Atmos-equipped cars worldwide…
written by Helen Raynor
directed by Douglas MacKinnon
music by Murray GoldCast: David Tennant (The Doctor), Catherine Tate (Donna Noble), Freema Agyeman (Dr. Martha Jones), Bernard Cribbins (Wilfred Mott), Jacqueline King (Sylvia Noble), Ryan Simpson (Luke Rattigan), Rupert Holliday Evans (Colonel Mace), Christopher Ryan (General Staal), Dan Starkey (Commander Skorr), Eleanor Matsuura (Jo Nakashima), Clive Standen (Private Harris), Wesley Theobald (Private Gray), Christian Cooke (Ross Jenkins), Rad Kaim (Worker), Elizabeth Ryder (Atmos voice)
Notes: The Sontarans last appeared with The Two Doctors (namely Colin Baker and Patrick Troughton) in 1985, though fanmade productions such as Mindgame and Shakedown revisited them after the cancellation of classic Doctor Who. This is the first episode to give, in dialogue, the revised name for UNIT – the Unified Intelligence Taskforce – which was changed from the original name, United Nations Intelligence Taskforce, for completely non-fictional legal reasons. Despite the change, dialogue elsewhere in the episode still says that UNIT gets its funding from the United Nations. Speaking of UNIT, a bit of fun is poked at the long-standing debate over whether the third Doctor‘s stint with UNIT took place in the 1970s or 1980s – and the issue certainly isn’t resolved. The Sontarans are apparently aware of the Time War, but for whatever reason were “not allowed to take part in it.” The reference to the human female’s “weak thorax” is a riff on the 1975 story The Sontaran Experiment, in which Field Major Styre noted differences in the thorax between the human genders.
LogBook entry & review by Earl Green
Review: For their handful of appearances in the classic series – a grand total of four stories – the Sontarans have certainly ignited the imagination of fandom down through the years, placing them in the upper echelons of favorite enemies from the original series. Their lust for war and their hyper-macho code of honor, and the cloned nature of their species, are interesting things to build on, along with their critical weaknesses. Perhaps moreso than any classic series villain revisited in 
the new series, the Sontarans are back, perfectly intact, and while their new costumes aren’t exactly identical to those of the original series, they look and sound a lot like their 1970s and ’80s counterparts.
That same fate isn’t, however, shared by UNIT. In the Torchwood episode Fragments, there was a clear implication that a change had taken place in the organization that the Brigadier once headed with a stiff upper lip and as few uniformed extras as allowed; “indefinite detention of enemy combatants” was now a staple of UNIT’s playbook. This episode makes that explicit with Donna’s reference to Guantanamo Bay, but what bugs me even more is Martha’s dialogue about changing UNIT for the better from the inside – in other words, she’s doing exactly what Captain Jack has been doing with Torchwood. Only Torchwood needed that change to its mandate; when and where and how did UNIT become this way? Even one momentary snippet of dialogue attributing this drastic change to 9/11 would satisfy me, because that’s the most likely answer; I guess now that we consider the post-Doomsday Torchwood to be good guys, UNIT’s now in the unenviable position of being the poster child for heavy-handed military tactics. Falling into Trap One, indeed.
Martha’s return is welcome, and it’s nice to see her get along with Donna instead of a rehash of the snippiness between Rose and Sarah. Another nice reversal is Donna’s return home, which is handled without the high drama of Aliens Of London or The Lazarus Experiment; instead, her absence has barely been noticed, and the scene where we’re reminded that Donna’s entire family has already met the Doctor in a variety of weird but completely unconnected circumstances is genuinely funny. Donna continues to be the best companion that the new series has given us yet, and her almost-huggable grandfather is the most sympathetic “companion’s family” character we’ve seen since Jackie Tyler.
I’m eagerly looking forward to the second part of this story, simply because The Sontaran Stratagem reminded me of how much I liked the Sontarans way back when.