Anyway, after the sleek opening credits, which look better in the shade, the Fringe division arrives on scene, and from the outside, things look a lot more straightforwardly destroyed. The theatre marquee is ripped in half, there are parts of the building on fire.

The Fringe team strolls through the wreckage, looking queasy as a man, whose torso has been separated from his legs, is carried out. Astrid shows everyone a video emailed by the security company that suggests the terrorists gained entrance from the side fire door. The alarm was disabled.

But there's good news, Astrid tells them, and she leads them to where they think they've found an "electralight." It must have been a dud, she says, and Peter holds it up. "We finally get to see one," he says.

Back at Fringe HQ, Peter works on the electralight while Astrid prattles on about how the "End of Days" was one of her father's favorite sermons: "When the world dies and a saviour arrives to end the suffering and usher all the worthy into heaven." Peter ignores her and asks for the alligator clips, and Astrid jokes that if her father ever met one of the kooks who's actually attempting to end the world, he'd probably kill them himself, and Peter continues to ignore her, so Astrid excuses herself with a stack of eyewitness statements and she'll tell Peter if she finds anything worthwhile. Olivia strolls over to see if Peter's figured anything out, but he hasn't. "Not only can I not tell you how the thing works, according to all the readings, it shouldn't be working at all," he says. Yeah, but... isn't it supposed to be a dud?

Anyway, Peter figures there's only one person on Earth who can tell them how the thing works. "Walter," says Olivia. Peter asks if she's got any markers she can call in, because he thinks it's past time.

Next thing we know, Peter's walking down a corridor flanked by a couple of guards in a high-security prison, and gets ready to meet... Walter, who shuffles into the meeting room in shackles and huge bushy beard and hair. It's very reminiscent of the first time we laid eyes on Walter Bishop, way back in the pilot.

After the commercial break, Walter puts his hand on the glass partition and Peter does likewise, and they smile sadly at each other. Walter jokes that it must be bad if they're letting Peter see him, and Peter says it is. "I heard a rumour that the sun was burning out. They don't tell me much in here," says Walter.