The Sontaran Stratagem/The Poison Sky in some ways feels like more of a modern story than it did at the time. The story features SatNavs used as weapons and SatNavs are arguably more commonplace today than in 2008, given that they are now installed in pretty much any modern car. After a call from Martha (Freema Ageyman) asking for him to return to Earth, the Doctor (David Tennant) and Donna Noble (Catherine Tate) arrive in 21st Century London to find that there have been a number of mysterious deaths that have all taken place at exactly the same time. The only connection is that they all had ATMOS installed into their cars. They team up with Martha's new workplace - UNIT - to find out why and discover the Sontarans are plotting to invade the Earth.

These are clearly a new clone batch of Sontarans, given that whilst they bear a close resemblance to their classic series counterparts their look is somewhat cleaner and a deeper shade of brown. Their ears are also more pointed, bearing more of an 'elf' appearance as opposed to the flat ears of the classic series.

Between the two, my preference lies with the new series look by prosthetics designer Neill Gorton. Their classic series appearance is certainly iconic but they perhaps bear too close to the infamous potato comparison. The new series Sontarans meanwhile appear more menacing; I find their appearance as a deadly warrior race more convincing compared to the classic series Sontarans. That's not to say I don't like the classic series Sontarans, just that the new series Sontarans have a stronger demeanour.

The other major difference with the new series Sontarans is their use of a catchphrase. Just like the Cybermen in Rise of the Cybermen/The Age of Steel the Sontarans this time round have been given a quotable phrase that they repeat over the course of the story. For the Cybermen, this was 'Delete'. The Sontarans have 'Sontar Ha!' Unlike some, I like the new series tendency to give characters catchphrases; it's a nice and quick way to establish the characters' personalities without the need of expositional dialogue. The Cybermen upgrade others to be like them, so their catchphrase is 'Delete' because they are 'deleting' the humanity of those who become Cybermen. Sontarans believe in honour and glory, so their catchphrase is a war chant.

There are plenty of similarities to be found between the Rise Cybermen and new series Sontarans, one important one being that the former are a new group of Cybermen from Pete's World created by a company known as Cybus Industries and the latter (as The Sontaran Ordeal explores) a Time War-era new clone batch of Sontarans. The new series Sontarans are therefore in my view different enough from their classic series iteration to be considered new monsters.

As for the story itself, it's definitely one of my favourites from David Tennant's time as the Doctor. The Sontaran Stratagem/The Poison Sky is an action-packed story that's a lot of fun to watch. The way it takes a modern device that can infamously become unreliable (SatNav systems) and turns it into a threat is genius. SatNavs can have the potential to be scary machines, especially when they try to send you off cliffs and it is therefore a marvellous idea by writer Helen Raynor (who got a lot of unfair comments directed towards her regarding her previous story for Doctor Who Daleks In Manhattan/Evolution of the Daleks) to include them in her story.

It definitely feels like a Sontaran story too. This is a strong update for the clone race and it is a shame that they haven't had a new series invasion story since. The Sontarans feel like a formidable threat for the Doctor and Donna, especially the way they manage to clone Martha Jones. I would have liked to have seen a follow-up story where they clone the Doctor; imagine an evil Doctor working for the Sontarans - wouldn't that be scary?

The Sontaran Stratagem/The Poison Sky stays true to how their previous classic series counterparts were characterised whilst also offering a new take on the race. Hopefully one day there will be a story exploring where Strax's loyalties lie: the Sontarans or the human race? I think that would be the best way to bring the Sontarans back now when Strax has been used for comic relief.

In the above paragraph, I mentioned clone Martha Jones. Clone Martha Jones is one of my favourite things about this story. Seeing a Doctor Who companion suddenly become evil is a fun thing for the show to explore; the series has done it before with Zygon Harry in Terror of the Zygons but the clone of Martha Jones in particular feels masterfully executed and a natural advancement for the plot. Freema Ageyman plays original Martha and evil Martha in such a believable way and I wouldn't be surprised if Jenna Coleman took inspiration for it for her dual role as Clara Oswald and Bonnie in last years' The Zygon Invasion/Inversion. Original Martha doesn't really get a lot to do but evil Martha is so entertaining to watch that you don't really notice Original Martha not featuring much in the plot.

And, of course, you've got the excellent Bernard Cribbins as Wilf. To me, Bernard Cribbins is the Doctor Who companion that never was. He sort-of had a companion role in The End of Time but it's hard to class him as a companion when it was only one story (I wish it had left it open so Wilf could have previously had more adventures in the TARDIS with the 10th Doctor). Wilf is such a loveable character, played with a stunning amount of charm by Bernard Cribbins and you find yourself totally invested and caring for the character when he becomes trapped in the car with the ATMOS smoke surrounding him. It's a relief when Sylvia (Jacqueline King) breaks him free from the car because you've grown to care for the character so much.

Overall, The Sontaran Stratagem/The Poison Sky is an exciting update for the Sontarans in the new series. Their use of a catchphrase and new look makes them feel significantly different from the classic series Sontarans and the story poses them as a credible threat for the tenth Doctor and Donna. Evil clone Martha Jones is fantastic and well-played by Freema Ageyman (sure to have been a blueprint for Jenna Coleman when she played her dual role of Bonnie/Clara). Then there's Bernard Cribbins as Wilf, who's just loveable as Donna's charming granddad Wilf and really should have been a companion for the Doctor.

The Sontaran Stratagem/The Poison Sky is one of David Tennant's best stories which David Tennant as usual gives an outstanding performance in again, proving why he is the best Doctor of them all. Catherine Tate continues to be strong as Donna Noble and I hope she continues to play the role for Big Finish. This is a Doctor Who two parter well-worth your time, whether you have seen the classic series Sontarans or not.