Curtis from 24 has been keeping himself busy stealing frozen heads from cryonics labs all over the country. But when his shapeshifter accomplice gets himself killed at a robbery right here in Massachusetts and bleeds mercury all over the place, the Fringe team is called in to investigate. Examining the body, Walter realizes that this guy is totally different from the person they thought was the dead shapeshifter who tried to kill Olivia, and now the team realizes her would-be killer could be anywhere -- and anyone. They're not yet aware that Fake Charlie is sucking down mercury to try and maintain his rapidly deteriorating fake body. So they look up an old experimental subject of Walter's, who he once drugged into having the ability to spot trans-dimensional invaders. She's willing to repeat the experiment. But when it comes time to ring a bell, it's Olivia who crumples. Having drunk a flatworm shake at Walter's suggestion to help retrieve her memory, she's already been having longer and more frequent flashbacks to her trips to the other side, and the bell triggers a full-length memory of her meeting with William Bell. Which we get to see.
Bell warned Olivia that the shapeshifters are looking for someone who has the power to open the door between universes -- someone who has a particular symbol on his neck. And Olivia has to find him first, to prevent what Bell calls the "storm." After Peter shocks Olivia back to the present, she rushes off to show that symbol to Nina Sharp, who is being quite helpful. But then Fake Charlie texts Olivia that Nina is the bad guy, just when Olivia remembers which lab the right head is in. And then she tells Fake Charlie, right before she discovers the Fake part. She just manages to kill him, but not before he passes word along.
As for Walter's test subject, there's clearly a mutual attraction, even though the way she now sees Peter clearly shows the repeat experiment was a failure -- or was it? In whatever case, Olivia also failed; the bad guys have the right head, and as the episode ends, it's knitting itself back onto a body while Curtis watches. Nice going, Olivia. One job, she had.
Wrapped-up, mummified, disembodied human heads are being loaded up into liquid nitrogen cylinders for shipping from a Medford, Massachusetts cryonics lab in the dead of night. Because why traffic in frozen noggins when decent people are awake? There are four uniformed men at the loading dock: two guys loading the back of the truck and plugging in the refrigeration units; a guy who tells "Kurt" that he doesn't "want these popsicles to melt;" and the aforementioned Kurt, who finishes signing for them and says they won't need to worry about that. We're supposed to think he's referring to how the cylinders are being hooked up to all manner of cryogenic whatever in the back of the truck, and a locking code is entered into the keypad once the door is pulled down. Just then a white Cadillac pulls into the alley. The two loaders, annoyed, step into the headlights, wondering what's up. After a moment, Roger Cross, who you might remember as preternaturally long-lived handsome black agent Curtis Manning from 24, steps out of the car and asks, "Hey, I was wondering if I could get some directions?" One of the loaders says he's trespassing and tries to turn him away. But Curtis, who seems cooperative at first, suddenly drops his half-eaten pear on the pavement, pulls two handguns out of the back of his pants, and plugs the two delivery men repeatedly. The lab guy scrambles for cover behind the truck, not realizing that "Kurt" is also in on it until Kurt shoots him. I think then he catches the snap, though. As Curtis gets the keys from him and climbs into the truck, Kurt tells him, "Let me know if he's in there. You know where to reach m--" He's rudely interrupted by a bullet to the back. Apparently one of the loaders wasn't quite dead yet, and he's shooting at Kurt from the ground. Curtis just drives off, leaving Kurt behind. Kurt struggles back to his feet, then stops another bullet, and another and another, each one rocking him a little bit less. Now he's just showing off. Would it be that hard to return fire? Finally he goes down for good when the fifth bullet hits him in the forehead. The guard who shot him finally succumbs to his own wounds. And the last thing he sees is Kurt, his head wound staining the pavement with blood that seems to be reflecting the silvery moonlight considerably more than is strictly normal.
Next morning, Astrid is doing some prep-work for Walter in the Fringe lab. Specifically, she's chopping up flatworms. Walter checks her work and tells her to keep chopping. He's happy to see Olivia when she walks in (now apparently fully healed and on her own two feet), and tells her his latest idea for helping her get her memories back. "I thought that we agreed that this was a stupid idea," Peter horns in. Over the noise of the blender Astrid is now running, because suddenly she's a production assistant on Fear Factor, Walter defends the idea. Which we still haven't heard yet, so Peter passes it along to Olivia, as bluntly as possible: "He wants you to eat worms." Walter explains to Olivia about an old experiment he did with William Bell, training flatworms to respond to light, and then feeding them to other flatworms, who absorbed the original flatworms' training. "It was Belly's idea." "Because who wouldn't think to do that?" Astrid cuts in, not looking up from decanting the worm slurry she's just made. Walter explains that the flatworms transferred their memories through ingestion. So by that logic, shouldn't Olivia eat herself? Peter and Walter descend into bickering over this, while behind them, Olivia just picks up the glass and sucks down its entire contents in one goopy gulp. Wow, somebody really wants her memories back, doesn't she? She's barely keeping it down as Astrid gets her some water and Walter says he was going to mix it with strawberries. Would that really be an improvement? Then they'd just be strawberry-flavored worms, and there'd be more of it to swallow. While Olivia continues to concentrate on not vomiting, the phone rings, and Astrid smirkily answers, "Bishop's Deli." Then her face goes serious. Like anyone ever calls the lab to hear bad jokes.