When a scientist falls dead after ingesting a lethal cloud of blue powder and his bones disintegrate in his body, the CDC suspects a biological attack. As the Fringe Team investigates further, a subject from Walter's past with ties to Olivia reluctantly agrees to assist with the intense case.
This episode's glyphs spell:
The Observer can be seen at the fundraiser where Olivia and Simon Phillips are undercover.
A blue recycle bin in 'Reciprocity' in the alleyway where Peter kills a fleeing shapeshifter is labeled with a "Powder Blue" sticker, foreshadowing the blue powder bioweapon used in 'Concentrate and Ask Again'.
The passing VW Beetle and Walter's focus on it in 'Concentrate And Ask Again' foreshadows Dr. Armand Silva's use of beetles in 'Immortality'.
The combination to Bell's safe in "Concentrate and Ask Again" was 0-5-2-0-1-0. This was the combination Walter used to access the daycare center in "Jacksonville".
Nina found a toy Monte Carlo in Bell's safe in "Concentrate and Ask Again". (Image 1)
Sam Weiss told her that in "Concentrate and Ask Again".