6. Earthling

Complete story — includes the ending

The Fringe Division is flummoxed by a case where victims are inexplicably disintegrated into ash. Broyles takes a particular interest in the case, as he worked on it in the past. He says that everyone who died had recently been to a hospital. The investigation leads the team to Russia, where they learn Fringe science is taking place in other countries as well. A man sent to space came back with a dark entity in him, which is stealing people's natural radiation, and killing them. Walter learns that the man and the entity are connected and cannot be separated, so Broyles kills the man to end the killings. However, the CIA reveals that the cosmonaut resurrected, and it is implied that he was sent into deep space, never to return.