This past segment of the story is the most satisfying strand. There's a very clever idea where the two aliens are on their own galactic witch hunt (having been persecuted for their own seemingly magic powers they've become twisted to the point of hunting out anything even remotely supernatural seeming and destroying it, so they're working through the proto-psychics on Earth) that mirrors that Kincaid is on. Having Simon Rouse, who of course gave one of the all time great Doctor Who performances as Hindle in the Peter Davison TV story Kinda, cut lose as Kincaid makes him an enjoyably OTT villain.
Mary's plot however, doesn't work as well. At the end of Part 1 the twins (who exist in both time zones) manipulate things so they steal the Tardis with her inside so they can return to 2011. She and Aleister then spend most of the remaining three episodes trying to avoid them and the “Witch”, with Portillon Jr. seemingly remarkably unphased by what's happening around him. There's little outright bad about these segments but it's also pretty much instantly forgettable.
Luckily the Doctor is able to keep things on track back in the past, as he uncovers the hidden spaceship of the aliens and is ultimately able to trap the younger versions of the twins on Earth (where they'll be stuck till 2011). Sadly if it seems that Agnes has been turned into the well monster in the process, meaning that, as we see her “death' in 2011 she winds up with one of the nastiest and most drawn out fates of any Doctor Who character, even if the “present” Twins wind up dying as well.
With Mary having used that old favourite standby of Doctor Who spin off media, The Fast Return Switch, to reunite with the Doctor we get a slightly forced “Happy” ending for Agnes as it turns out the creature in the well wasn't her at all but a technobabble mutated doppelgänger. Whilst this does undo some of the power of her death, the Doctor's final thoughts on how the cosmic witch hunt could have adversely affected the evolution of humanity by killing off so many people showing the beginnings of the next stage means it's not all sugary happiness at the end.
Despite the present day plot being less exciting, strong writing in the past and great performances from all involved means this stays great fun, and Julie Cox is already feeling like an old hand at this.
Three Pointy Hats Out of Five.