This episode centers on the Fringe team's investigation into a series of robberies of the element osmium which they connect to a scientist who is able to defy the laws of physics in an attempt to allow his paraplegic son to walk again.
This episode's glyphs spell:
The Observer can be seen in the crowd outside the Massachusetts Metal Depository.
The periodic table of elements in the Jacksonville daycare center in 'Subject 13' displays the element Osmium, the element featured in 'Os'.
A control box in 'OS' has a logo for "Gray Electric" with a lightning bolt symbol. This foreshadows the main suspect in 'Stowaway', Dana Gray, who had been struck by lightning multiple times.
This is similar to William Bell's 'Soul Magnets' experiment that was enacted in "Os".
Suddenly she found herself drinking tea, disoriented from the timeslips.
Bell put his soul magnets into the tea that Olivia drank. (Image 1)
In "Os" the team learned that Bell had enacted his Soul Magnet plan before death using Olivia as a host.
In "The Last Sam Weiss" a new parchment ("The Crowbar") was discovered that had Olivia's face on it. (Image 1)