They apparently rush right over to the lab, and Walter starts off with the bad news: "The shapeshifter's blood is 47% mercury." As opposed to that of the first shapeshifter, who had a perfectly normal blood sample. Which indicates that the first shapeshifter wasn't one at all; and that the actual shapeshifter is probably still around, and could be disguised as anyone. "And you could still be in danger," Walter says. Then he reveals the good news: "I think I may know how to find him."
If you were hoping for Olivia, Peter, Walter, and Astrid to start spiraling into paranoid accusations against each other like something out of The Faculty, you'll be disappointed. Or at least, I was. Instead, Walter replays them the old, grainy videotape of his experiment on Rebecca Kibner, whose head he pharmaceutically fucked with back in the day. On the screen, young Rebecca trips out, talking about "a soldier from somewhere else... a glowing man... he's from a other universe, man!" Walter thinks that since he helped her spot shapeshifters once, he can do it again. This seems a little sketchy to me. How hard can it be to find people who are half mercury? Wouldn't it make more sense to get a portable MRI scanner, cart it around the city, and arrest anyone who sticks to it?
Footnote: Yes, I know that wouldn't actually work.
Walking across the grounds, Olivia is on her cell phone to Gnarlie, updating him on their "progress" and asking him to ask Broyles for anything new from the crime scene. I'm sure Broyles will be impressed with Olivia's investigative acumen. "Sure thing," Gnarlie responds, and hangs up before she notices that his voice is all fucked up. He's currently in a drugstore, and he throws a slushie and a big batch of mercury thermometers down on the counter. Can you even get those any more, let alone a dozen or more at a shot? "Starting your own pharmacy?" the kid behind the counter "jokes." Gnarlie's only response is a cadaverous glare and a sharp, hostile noise from somewhere deep in his sinuses. It totally works, though. I'm going to start doing that with wise-ass cashiers myself.
Out in his car, Gnarlie dumps the slushie out the window, and breaks all the thermometers into the empty cup in one splintery bundle, his face twitching unnaturally as he does so. After sucking down the silvery cocktail, which can't be more than a tablespoon or so, he convulses some more, then watches in the mirror as his loose eye socket tightens back up. And then the glass he swallowed with the mercury kills him. Okay, it doesn't but it should.