During the 2005 revival, Doctor Who has cast many well known faces as its companions. From Billie Piper (famous for her teen pop star career) to more recently Bradley Walsh, there has been quite a large variety of actors playing the role of the Doctor's assistant who have been known to the public. Before the current run of the show came to fruition, however, there was John Nathan Turner's decision to cast Bonnie Langford as Melanie Bush, a popular child star known particularly for her work as a dancer.

She's introduced in the strangest of ways here. Rather than her introduction story coming in the form of a typical narrative on how she came to meet the Doctor (Colin Baker), we skip ahead to her already travelling with the sixth incarnation of the Time Lord. It's unusual, but in the context of the narrative it works, because the Doctor - through trying to find evidence for his defence in his courtroom trial - isn't looking specifically for the start of his adventures with Mel. He's looking for something to best sell his case that he is innocent of all charges thrown against him. It would have been more than a little coincidental if the best suited adventure for that purpose happened to be Mel's first.

The Doctor gives us one hell of a story here too. Following a distress call, he arrives with Mel on a luxury space liner, where they find a series of murders being committed by a mysterious killer. The Doctor and Mel must locate the source of the distress signal as well as the identity of the murderer before it is too late. It's your typical Agatha Christie-style whodunnit, posing two highly enthralling mysteries which have very satisfying conclusions later into the narrative. The Russell T Davies era may have done an Agatha Christie murder mystery in its fourth series, but Terror Of The Vervoids is arguably the Proto-Unicorn And The Wasp.

The eventual reveal of who the killer is works a charm. It turns out that professor Sarah Lasky's (Honor Blackman) assistant Doland (Malcolm Tierney) is the man responsible for the murders onboard the space liner. Like all of the best reveals in murder mystery storylines, it hits the sweet spot of the culprit not being too obvious whilst not being considerably left field to the point where his involvement is unbelievable either. It makes sense without being an easy conclusion to reach. It's also clear how the Doctor was able to reach this conclusion that he was the man responsible, as the narrative explains his reasoning in a clear and concise manner.

Doland is not the only evil presence onboard the space liner however. There's also the titular monsters of this adventure, the Vervoids. These creatures are among my absolute favourites in the classic series of Doctor Who; they have an extremely effective design which neatly conveys the appearance of vegetation, and their motives are understandable and somewhat sympathetic, given that their actions - whilst wrong - essentially boil down to a fight to survive. As the Doctor puts it, it's 'kill or be killed'. Plant life like the Vervoids are constantly under threat from 'animal kind', whether it be animals such as giraffes or elephants eating them as food or human beings removing weeds from their gardens. By fighting 'animal kind', therefore, they are really just fighting for self-preservation. It's not much different to the food chain of lions or tigers hunting their prey.

The courtroom scenes here are also some of the best so far. This serial gives us a tantalising hint at the Matrix having been tampered with and manipulated by the Valeyard (Michael Jayston), with some scenes having been changed from when the Doctor viewed the adventure in the Matrix. It's a really great way to keep viewers invested in the courtroom drama, as you find yourself desperate to find out just what the Valeyard has been up to. Is the Doctor right with his theory, or are his suspicions totally unfounded? You could imagine viewers at the time even contemplating the possibility that it is a distraction tactic by the Doctor to buy himself time whilst he thinks of a way to clear his name.

The story ends on one hell of a cliffhanger, as the Valeyard declares that the charges against the Doctor are now for 'genocide' rather than simply interference in the affairs of other beings. This is in relation to the Doctor wiping out the entire Vervoid race at the end of the serial with a device that causes them to experience all of the seasons at the same time, and it's definitely hard to argue with him here. The Doctor's actions are somewhat questionable - then again, it could be a manipulation of the Matrix - and it really feels as though the Doctor could end up punished for his crimes. He's in the worst possible position for sure, leaving us with an extremely effective lead-in to the final two episodes of this 'Trial Of A Time Lord' serial arc.

Overall, 'Terror Of The Vervoids' is easily Colin Baker's greatest Doctor Who serial. Playing largely like an early prototype for 'The Unicorn And The Wasp', it provides us with a gripping murder mystery on board of a luxury space liner, and one of the classic series greatest ever one-off monsters in the Vervoids. It's also nice to see Bonnie Langford make her first screen debut as Melanie Bush, a companion who I feel gets too much undeserved hate from the fandom; Bonnie Langford is brilliant in her introduction, and brings so much energy and presence to her first appearance in the role. 'Terror Of The Vervoids', in short, is what Colin Baker's era should have been, and it's a shame he didn't get more stories of this quality during his tenure.