Previously on Doctor Who, the Doctor, Mel and Hebe’s new friend Professor Patricia McBride (Imogen Stubbs) outed herself as a eugenicist bigot, stole a time travelling suit and set about creating an alternate timeline where disabled people were completely eradicated. In the process, she deleted Hebe from history, prompting the Doctor and Mel to set off in the TARDIS to find out what happened to her. And it is in the midst of this mission that we find them at the start of Purity Unleashed…

Well, sort of. Matthew Sweet‘s Broadway Belongs to Me! is pretty much a standalone story, deviating almost completely from the Hebe/Patricia storyline. This tale takes the Doctor and Mel to 1930s New York, where they become involved with Behold America!, a new musical set in a future Fascist United States. It’s an offbeat story, heightened in tone from the music to the performances, but it’s an enjoyable listen, particularly because it taps into Bonnie Langford‘s theatrical and musical roots.

Despite all that, though, the story feels like little more than treading water, just a means of delaying the search for Hebe until the next episode. The cliffhanger to the previous boxset was, in all honesty, one of the only enjoyable things about it, so to have that thread immediately dropped is more than a little disappointing, especially for an episode which, outside of the fun musical bits, is on the weaker side. Oh well, onwards and upwards!

Next up is Chris Chapman‘s Purification, a time-hopping tale which reintroduces the misguided Patricia McBride as she attempts to make a ‘better’ world: one without disabled people in it. It’s a fast-paced, action-packed script kind of like The Chase crossed with Listen, taking us all throughout history as Patricia’s masterplan continues to unfold.

Imogen Stubbs is really given the opportunity to get to the heart of her character with this one; her relationships with not only the Doctor and Mel, but also with several of this story’s side characters, are put front and centre, giving us an insight into her motivations and the way she views both the world and the people around her. This is really strong stuff, building to an almighty crescendo which sets up the final episode with flair.

And what a final episode! Ian Potter‘s Time-Burst takes us to Sheffield, 1864, where the Doctor and Mel are caught up in a series of time distortions caused by Patricia’s meddling. As the Doctor is flung throughout time, Mel meets a young couple who have become embroiled in strange goings-on at the local steelworks; goings on that may be linked to Patricia. And with the devastation of the Great Sheffield Flood on the horizon, the odds are very much stacked against them.

This is a slow-paced but highly enjoyable tale, giving us an insight into a little-known historical event while furthering the Purity plotline in some rather unexpected ways. This definitely isn’t the climactic finale you might expect, but it really does work, and is perhaps the strongest of this new run of Sixth Doctor Adventures since they began last year. Colin Baker, Bonnie Langford and Imogen Stubbs are on sizzling form throughout and, complemented by likeable turns from guest stars Luke R Francis and Billie Fulford-Brown, this only adds to this story’s success.

In keeping with the rest of this series, Purity Unleashed ends on a cliffhanger, and this is another doozy, setting up what promises to be a thrilling continuation of the story come August. And, while this set isn’t perfect, it’s certainly an improvement on last year’s offerings, so I’m highly looking forward to hearing more in a couple of months.

Purity Unleashed is available on CD or as a download from http://www.bigfinish.com