"Oh well, I've had a good innings. This regeneration is a bit of a clerical error, anyway."
IN THIS ONE... The Doctor creates a boot strap paradox to beat the Fisher King.
REVIEW: Now this is how you make a two-parter that doesn't feel like it's been padded. Two time frame/locations, two types of stories interlinked (base under siege and paradox mystery), and a large cast whose members get to shine in different episodes. It starts with the breaking of the fourth wall, and the Doctor explaining what a boot strap paradox is to the viewers (an episode later this season kind of explains this behavior, but only kind of), and we will obviously see one unfold. Does it blow the surprise? Was there one? My own brain is wired for it, and has been since I read an adventure novel as a kid that had the heroes doing just this kind of thing. So I tend to think of self-fulfilling prophecies as viable solutions in time travel narratives, and am always a bit sad when they're not used (the previous two-parter, for example, used it too little). I don't care if I see it coming, but the exercise itself makes me happy. And the Doctor's explanation is fun regardless, sends us into the opening credits with an awesome rock remix of the title tune, and allows for a very cheeky shrug at the very end of the episode.
So to explain it, yes, once the Doctor finds out he's going to die and become a ghost, he decides to MAKE this happen. He changes nothing of the established future, just its interpretation. Remember the Clara hologram in the previous episode? Well, I didn't, and of course, that's what this Doctor is. And of course, he's got to be in the suspended animation casket. I don't think those were any surprise to me first time round. But he's still go to work it out, just as Clara has her own puzzles in her time frame. More of her osmotic relationship with the Doctor - she asks people to put their lives at risk and is called on it by Cass, who is still a strong a character as she was in Under the Lake. O'Donnell and Bennett take on their full three-dimensionality as they travel back to 1980 with the Doctor. She gives us a nice twist on "it's bigger on the inside", and is both forceful and fannish without being irritating, which past characters with those traits haven't always managed. When she dies, Bennett gets a blazing speech accusing the Doctor of using her to test his theory that the list of names recited by his ghost are a chronology of the dead. It's perhaps unfortunate that the final moment with this crew are about revealing they're all in love with one another, which I thought they'd nicely sidestepped there. But not that big a problem.
The villain of the piece is the Fisher King, a mostly impressive 10-foot monster, completely alienating in looks, though perhaps a bit bouncy in the shell area. He's a total badass - we saw what he could do - and about as evil, even demonic, as any of the Doctor's old enemies. He's violated life and death, and made the Doctor very cross, and so he deserves to die in a funny way. The Fisher King just looks on as the dam breaks (explaining where the ship's power cell went) and he's washed away. It's yet another twist that the bad guy was dead 150 years before the adventure even began. They don't really manage to make the fake Russian village, a Cold War training ground for British agents, more than a thematic play on the seasonal arc, i.e. the idea that things are not as they seem, and that villains and heroes can be interchangeable. Kind of a waste of an interesting location. But despite its small flaws, Before the Flood succeeds as a piece of plotting, acting and direction. In the latter category, it's got some nice atmospheric photography and great suspense sequences (like the bit where the deaf Cass is being followed by a ghost trailing an axe).
THEORIES: It's just dawned on me that the mural in the base, of a snake-like dragon holding a Viking ship, may be a reference to the next episode. Another thing. The TARDIS refuses to allow the Doctor to return to the future and prevent his own death that way, and later the Fisher King seems to infer that the Time Lords became fearsome warriors AND YET the Doctor is a curiosity who cares about not changing history. In other words, while older Time Lord technology (like an old Type-40 TARDIS) has built-in failsafes to protect the time stream, Battle TARDISes and the like from the Time War COULD change history. It's obvious, hasn't really been discussed before. What made the Time Lord Victorious so dangerous and terrifying is that he was taking on the worst features of his people from the Time War (and possibly strategies adopted by the War Doctor). That gives the Doctor a psychological block when it comes to "breaking the rules", as much as a technical one.
REWATCHABILITY: Medium-High-Plus - I could do without the romance button at the end, but I love this episode for its great use of time travel, its neat monster, its strong character bits, and its moody (but also cheeky) direction. Your mileage will only vary if you're very sick of the timey-wimey Moffat era.