It all starts with a simple job; break into a system where time has ceased to exist and help out an old University chum. Well… acquaintance. But as River finds out, the past doesn’t just refuse to stay buried, it has teeth, claws, heavy weapons and will reprogram itself until it finds a way to end her.

This is one of those seasons that sneaks up on you. ‘Time in a Bottle’, by Emma Reeves and Matt Fitton is a big part of how it manages it too. A deceptively simple story, it introduces some delightful hints of River’s university years, a wonderful supporting (Spod The Warborg is a standout) and a massive twist at the halfway mark you never see coming. Simultaneously a smaller, and much larger, story than it seems it sets up what follows with an ease that only impresses the further on you go through the season. George Asprey’s Melak is an especially good, Weasley villain too.

‘Kings of Infinite Space’ by Donald McLeary cleverly builds on this and invokes one of Doctor Who’s sacred plot structures: the chase. Fleeing with her new found companions, River finds herself outmanoeuvred at every turn and slowly, the tone of the episode shifts from dread to outright horror. This really could be it; the Discordia really do seem to have River’s number and the increasingly desperate gambits she’s forced into buy her ever decreasing amounts of time. This is unflinchingly grim stuff and it works beautifully because of that as well as an extremely strong supporting cast. Adele Lynch’s Gammarae, a warrior ant security specialist and Josh Bolt’s Spod get a lot of especially great stuff here. If the first story is set up, then this is the reveal and it’s fiercely effective.

‘Whodunnit?’ by Matt Fitton is where the season rolls the dice. There’s a massive ask of the audience here as in short order we’re introduced to Melody Malone as opposed to River, a Mr Samsa and a variety of distinctly familiar detectives all gathered in an old house during a storm…The episode trusts you to jump into the deep end and swim and you do because again the performances just carry you along. Better still, the payoff here is incredibly clever and gives you a better insight than very nearly everything else we’ve had so far into how River thinks. It also uses the Doctor in one of the smartest ways I’ve ever seen, simultaneously casting them in their classic ‘heroic intervention’ role and having that role mean something immensely different. Funny, bleak, clever and Tim Bentinck is extraordinarily good as Samsa.

‘Someone I Once Knew’ by John Dorney has the near impossible task of rounding all this off and introducing the Fourth Doctor and his relationship with River. It succeeds on every front especially the interplay between the two leads. Baker is on top form here and 4 and River have a similar energy to 4 and Romana, albeit with a far more affectionate edge. The reasons why he can be here, and why this has never come up before, feel earned rather than constructed and the story itself brings the Discordia into land in a manner that cleverly evokes several eras of the TV show at once. If there’s a criticism here it’s that this is all perhaps a little too Moffatian. The tower of ideas the season is built on gets very high at times but never quite wobbles. Instead, you’re left with a story that’s taken River to Hell and back, explored who she is and why and delivered a memorably nuanced set of villains into the world.

Verdict: Unapologetically complex, literate and very funny in places, this is an intensely ambitious and epic story told over four plays. It’s also a deep exploration of River herself, and a surprisingly tender romance. Epic in scope, successful in execution and a welcome addition to the Diaries. 9/10

Alasdair Stuart