A highway construction worker is the seventh in a series of mysterious disappearances in Lansdale, PA. The team come to investigate and finds traces of a mysterious paralytic. Meanwhile, Walter tries to send frogs to an alternate reality and Olivia realizes her recent trip has altered her in ways she can barely understand.

When an American officer who served in Iraq blows up in a Philadelphia train station, the Fringe Division investigates and determines that something turned the man into a living bomb. Peter and Olivia travel to Iraq to determine if Peter's contacts can shed some light on the situation.

A man in Seattle goes berserk, attacking his boss and claiming his victim is a demon. After the killer dies of what appears to be exhaustion, the Fringe Division discover it's only the first in a series of killings where the persons initiating the attacks were in a dreaming state while awake

A healthy woman dies of rapid-onset cancer in a matter of minutes, and the Fringe team is called in to investigate. The killer has connections to Jacksonville... and Olivia is a potential victim. Meanwhile, Olivia tries to come to terms with her knowledge of Peter's origins.

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.

The beginning of the end is triggered when Walternate finds a way to wreak havoc “over here."

As devastation spreads on This Side, Walter, Olivia, and Sam Weiss struggle to find a way to stop the destruction and discover that one individual has the ability to allow Peter access to the Machine.