The Doctor, the Tylers and Mrs. Moore crouch behind garbage and watch the monsters pass. Rose holds Pete's hand tightly (watch for that in future -- clinging to their hands like that). The Cybermen stop at the garbage, but the Doctor bleeps at them with his screwdriver and they continue on. I think a good time to engage the anti-Cyberman setting on the screwdriver might have been, oh, any time in the last hour and a half. Rose stands, letting go of Pete, and he stares at her, very highly confused by her behavior. They watch the Cybermen heading into the horizon and, at the Doctor's word, creep out and run in the opposite direction.

A group of EarPod zombies -- including Jackie -- climbs out of a truck and a Cyberman speaks: "Chamber twelve now closed for sterilization. All reject stock will be incinerated." I like Jackie and all, but this one? Reject stock indeed. (On the other side of Hell we burn off what doesn't work. It hurts, but it's the other side of grace.)

The Cybermen chase Rickey, cornering him at an alley, and he finds himself at a chain-link gate, which is locked. On the other side of the fence is Mickey, terrified, watching his better self pursued by demons. And he screams. Rickey climbs the fence, but not quickly enough. They grab him by the ankle and he is lit with blue fire. And he screams. Mickey watches this happen, watches himself die, and in the silence, he stares. The Cybermen watch him, standing still at the site of his own murder. He cries, and he stumbles, and he runs.

The etymology for the constant π comes from the fact that it's the first letter of the words periphereia (periphery), and perimetros, (perimeter). But it's also the first letter in peripateia, which defines this show and always has; periphrasis, which defines Rose, and Ten as well, and only means anything when you apply it to love; perishable, which ditto Rose and Ten, but only by half; periscope, which is how he sees the world, and perinatal, which is what he still is; periodicity and the Siege Perilous, which is what the season's about; perineum, the no-place between the worlds of divinity and excretion, inspiration and burning off what's not needed, breathing in and breathing out; perigon, or an angle equal to 360 degrees, coming back home; periapt, Ten being the charm she wears against danger even though she never needed it; perikardios, around the heart we're circling; perigee and perihelion and perilune, the closest you can be to the Earth, to the sun and the moon, without touching them, without falling in; and peri, a word with which we're familiar: the angel that has fallen, the fairy that takes you away. (And the person who played this game with the Doctor in the Big Finish serial "...Ish," a.k.a. the Who story written precisely for Jacob.)