Having taken a little break from our rewatch run, in order to concentrate on the latest series, we return to rebooted Doctor's fourth season, for it's first two-part story. Oddly, that meant that I watched the Sontaran's return to the series, having just watched them successfully invade Earth some 13 years later.
Martha Jones, (Freema Agyeman) now a UNIT agent, recalls The Doctor (David Tennant) to Earth to help investigate a string of deaths linked to ATMOS, a newly released device that lowers car emissions to zero. Though the device is invented by teenage genius Luke Rattigan (Ryan Sampson) the Doctor firmly believes that the technology is too far advanced and must be alien in origin.
The Sontaran's are amongst the strangest of the Doctor's pantheon of villains. They do, as the show points out, look like a baked potato in a space suit. This is not to say that the effect isn't reasonably well realised here. Christopher Ryan and Dan Starkey, who play the principle two in this episode would go on to play various Sontarans whenever the characters appeared.
This episode is really the one to watch for actors who would make it in other shows. Ryan Sampson is now on "Brassic", Clive Standen would play a key role in "Vikings". The pre-credits scene even has an early death for "The Walking Dead's" Eleanor Matsuura. It's selling point though is probably the return of Martha, who gets to meet another companion, though she and Donna get on well - presumably as Donna hasn't any romantic feelings for The Doctor.
It's a two-part episode, so this is mostly set up for aspects to be paid off next time. There are some funny moments and a few other bits of silliness that let the episode down a little. It's not awful though.