Acting as a break between the two Nerva Beacon stories The Ark In Space and Revenge of the Cybermen, The Sontaran Experiment is another one of those odd classic series stories like The Edge of Destruction that form only two episodes rather than at least four. This two parter is the very definition of 'filler'. It feels as though it's just there for the sake of being there.

The Sontaran Experiment follows Sontaran Field Major Styre experimenting on a bunch of astronauts who were brought to a deserted Earth by a fake distress call. The story is badly paced throughout and very dull to watch (something I hate saying about a story from my favourite show). The Sontaran in question doesn't even appear until the end of episode one and even then he never feels like much of a presence or threat to any of the characters. There's not enough story to fit 45 minutes; if anything, it would have been better as a single 25 minute episode as that's all there's enough plot for. At least The Edge of Destruction had more story to it. This one's like it was cobbled together because they suddenly realised they needed two episodes between the previous and next four parter.

The Sontarans are usually great villains but here Field Major Styre feels as though he's only there as a cheap option as they already had the costume made from The Time Warrior. The Sonataran presence really isn't justified; it could be any monster there and it wouldn't make much difference. The only neat thing about Field Major Styre being the antagonist is how it links in to Sarah Jane's first appearance meaning there is history between the companion and the alien race. That's one thing another monster wouldn't have provided.

Speaking of Sarah Jane, Elisabeth Sladen is brilliant and it really shows why she's still arguably the most iconic Doctor Who companion after K-9. In fact, if there's any saving grace for this serial it's the cast. All are on top form, from Tom Baker as the Doctor to Ian Marter as Harry Sullivan. They nearly make it feel like you haven't wasted time watching this serial. It's a shame director Rodney Bennett lets them down however with his poor direction. Everything feels a little amateur and due to the positioning of the actors by Rodney every shot feels bland. There is nothing engaging about the directing in this serial and with a weak story it really could have benefitted from some great direction.

Overall, The Sontaran Experiment is a dull 45 minute story with poor direction, a bad pace and a pointless use of a Sontaran villain with Field Major Styre. It does, however, contain great performances from the TARDIS crew of the time Tom Baker, Elisabeth Sladen and Ian Marter.