Human beings are reduced to ash statues and Broyles realizes that the same person responsible murdered five other persons four years ago... a case that he never solved.

A Dutch industrial consultant arrives for an appointment and dies in a painful explosion of blood. Olivia and Peter arrive on the scene first and discover that the blood contains a pathogen and everyone in the building may be contaminated. While Walter and Astrid work outside the quarantined building to create a cure, the virus develops unique characteristics that pose a danger to the entire world.

When the passengers on a commuter train all die instantly of massive power loss, the team realizes that a time traveler is responsible... and that it may be impossible to apprehend him. Meanwhile, Walter writes a letter to Peter explaining his origins.