As CBBC’s Wizards Vs Aliens approaches the end of its first series, the show poses an ethical conundrum; and also posing a threat to the friendship at the core of the show.

Kicking off the first part of ‘Fall of the Nekross’, we get a neat reminder of two of the show’s main features: Ursula, wizard Tom’s grandma, and her knack for not getting spells quite right (here, only managing to move the Nekross ship a few metres rather than banishing it to outer space); and those nasty aliens themselves and just how vile they can be. We are shown a poor Japanese girl have her magic extracted, and thus becoming an old woman.

It’s vital that we’re reminded of just how bad the Nekross are because this forms a central theme in this story from Doctor Who and The Sarah Jane Adventures writer, Gareth Roberts. In the world of Who, Roberts is known for his more rompier jaunts such as the brilliant ‘The Unicorn and the Wasp’ and ‘The Lodger’, but, as he showed so well in SJA’s ‘The Last Temptation of Sarah Jane Smith’ and ‘The Wedding of Sarah Jane Smith’, the writer tackles moral dilemmas with sensitivity and thought.

And a moral dilemma is at the very heart of the penultimate Series 1 story. Science ‘geek’ Benny has discovered a way to despatch our alien invaders through technology, using a computer virus (old skool, man), but his laptop lampooning does its job too well. Rather than forcing the Nekross away, the virus has debilitated their ship, the Zarantulus – so much so that all aboard will die. Although the wizards seem to be ok with this, Benny is most definitely not. Once aware of their perilous situation, the young boy is immediately remorseful.

This is quite the turn of events for Wizards Vs Aliens. Writer Roberts directly asks us who we sympathise with. Are we onboard with Ursula, happy to see the enemy gone – whatever the cost of life? Or, like Benny, do we engage in compassion and take the higher ground? It’s a fascinating conundrum, with Ursula coming off as a Belgrano-sinking Thatcher-type and some of the audience may genuinely wonder why the rules of war won’t allow for the Nekross to be destroyed.

Of course, Ursula sees the light; though you may well disagree with that – remember, the Nekross are a bad, bad bunch (we’ll see no better proof of this than in next week’s finale). Even after Benny rescues the Zarantulus, Varg is more than happy to kill the teenager.

Once morally reunited, Tom and Benny embark on helping out the Nekross (the former spurred on by his relationship with Lexi, explored in last week’s story) with the boy wizard utilising the stone circle first seen in the opening episodes.

Director Joss Agnew injects a shudder full of horror into these moments, using excellent POV camerawork to bring the stones to life and visualising Tom’s fear. Lending a hand, or a voice rather, is Gabriel Woolf – known to Who fans as Sutekh in ‘Pyramids of Mars’ and The Beast in ‘The Impossible Planet’ – who does a terrific job in making these standing rocks so terrifying as the Voice of the Stones.

The Stones themselves are a cracking addition to the show’s mythology and make for an impressive villain, even more so than the Nekross themselves. You get the feeling that those guys could raise some real hairy havoc for the wizards in the future, and seem to posses a knowledge beyond their realm leaving with a very Russell T Davies-esque prophecy (though looks like we only have to what until next week to see it fulfilled).

As with The Sarah Jane Adventures, Gareth Roberts tackles adult themes whilst laying on the thrills with a splattering of chills and intrigue. ‘Fall of the Nekross’ has the grand feel of a finale and ramps up the drama and mystery for next week’s climactic series end with the reveal of the aliens’ “master plan”.

Aired on Monday 26 and Tuesday 27 November 2012 on CBBC.

> Order Series 1 on DVD on Amazon.

What do you think of Wizards vs Aliens so far? Let us know below…