There were moments during Co-Owner of a Lonely Heart when Philippa Langdale’s camerawork was so elastic it almost threatened to bring this particular reviewer out in a case of the giddies. But that’s probably just an age thing showing, because what this fourth episode of Class was quietly achieving in the meantime was an effortless demonstration of how the series is going to function in the longer term. Rather than a succession of simple Monster of the Week plots bookended by the Arc Introduction and the Grand Finale, instead Patrick Ness has re-introduced us to the Big Bad and the underlying narrative trajectory in the first half of a two-part story marking the mid-point of the programme’s first run.

Ness’ real achievement is in having at least three external plot-lines – which may or may not yet prove to all be inter-connected – vying for space in just a little over forty minutes of screen-time, without diminishing the impact of any, nor upsetting the tone of the episode as we switched between stories. To then go ahead and include another, more personal, storyline beyond those and to make sure it had the space and time it needed to function was a mark of how well-prepared Class has actually turned out to be. After that rather clumsy and over-stuffed first instalment, this not-quite-spin-off has been improving week on week to the point that you now have to remind yourself every once in a while that it still takes place in the same setting as An Unearthly Child did those 53 years ago. Peter Capaldi’s appearance only three weeks back now feels like a blip on a horizon long since traversed.

So, Week Four was April’s turn at the heart of proceedings, with Ness returning to the situation he created in For Tonight We Might Die much sooner than most would have anticipated. Outside of the sci-fi, April’s father returns to the family he unfolded, and we learn he isn’t perhaps the monster she painted him as. It’s all about interpersonal triangles this week, with April and Ram consummating their quite tender fledgling relationship ahead of an uncomfortable confrontation with April’s mother, and yet another leg-related miracle in what could prove to be something of an inadvertent running theme. Or maybe just a walking one, as Ram’s curricular physical prowess seems to have been left at the door to the Hellgate along with his tattoo-bearing coach.

If the emotional material is all rather earnest and intense – par for the course in teen-targeted fiction it seems – the rest of Co-Owner of a Lonely Heart makes room for subtlety and dextrous storytelling. Following an encounter with a robot two episodes ago, and an intriguing reference to “the Governors” last instalment, this week Miss Quill comes face to face with what looks to be something of a covert and loitering threat in the shape of Dorothea Ames, played by the redoubtable Pooky Quesnel in a spark-flying manner that suggests Quill might have met herself a match. Let’s hope Quesnel sticks around beyond next week’s Brave-ish Heart and injects some more much needed levity into the series.

Elsewhere there’s a rather subdued foliar alien invasion, playing out like an extended version of the opening to Philip Kaufman’s 1978 Invasion of the Body Snatchers, yet with a menace that was spelled out with economy and precision. It’s impossible to tell where Ness will take things next, with Episode Five promising to be something of an adventure-heavy mid-series peak, but his willingness not to draw anything out beyond a pre-engagement introduction demonstrates a lightness on its feet and readiness to wrong-foot that is beginning to make Class a compulsive watch.

Perhaps the only evidence of clumsiness was in the way Ness switched between events in Coal Hill and those on the other side of the cosmos, albeit necessarily so for fear of sacrificing the all-important symmetries between April and her arch-nemesis Corakinus. The scenes set in the Shadow Kingdom felt at odds with the domesticity on display elsewhere, and might have been better left to the imagination ahead of events imminently subsequent. Brave-ish Heart would have come as so much more a surprise had we not already been introduced to its battleground.

But that’s a minor quibble. With its continuing improvements and a number of variously compelling plotlines, Class is now shedding the accoutrements of its influences and finding its own place in the universe.