Fringe

 Good news, bad news.  The bad news is that Walter has discovered the corpse's blood is 47% mercury.  Why is this important?  Because the first shapeshifter he autopsied (the nurse) had only traces of mercury.  Which means... she was a victim, not a shapeshifter.  The real shapeshifter is still out there somewhere.

The good news is that they may have a way to find him.  Rebecca Kidner, one of Walter's past experiments, took a bunch of LSD 20 years ago and saw people's auras.  She could sense the difference of auras of people from the other side.  Perhaps she still can.

Olivia calls Not-Charlie to tell him that they might have a lead on the shapeshifter.  Obviously, not a good one, since he is the shapeshifter, but still.  Not-Charlie isn't doing too well.  He buys a dozen mercury thermometers, cracks them open and drinks the quicksilver.  He needs it to maintain his form.

Olivia takes the insta-disguise device to Nina Sharp.  She tells her that the device seems to be streaming information.  They believe that it is the image of the last person the shapeshifter took.  Nina's tech says that he can reconstruct the images - even on the broken device - now that he has a functioning one to work off of.

Meanwhile, Peter and Walter track down Rebecca.  She is more than pleased to see Walter.  It seems that she is still hot for teacher.  Unfortunately, her powers faded after the first couple years.   She is more than willing, however, to be shot full of LSD again to see if they come back.

Back at the lab, everyone preps Rebecca for her acid trip.  Concurrently, Astrid is receiving the streaming rendering of the shapeshifter's last victim.   Before Rebecca goes under, she tells Peter that she remembers seeing him when he was just a young lad.  Walter tells Peter to ring a bell to help put Rebecca into a suggestible state.  Peter does and Olivia collapses like her strings were cut.  Hello, Pavlov.