The episode received acclaim from critics who highlighted the performance of Anna Torv's double duty, guest star John Pyper-Ferguson, as well as the exploration of the parallel universe and the use of love and sentimentality that leads to different lifestyle choices.

He offers to help, and willingly takes a tranquilizer that puts him to sleep during the transport to the parallel universe through the Machine Room bridge.

During his abusive childhood, he experienced homicidal urges which he attempted to sate by killing small creatures; he mentions a change in his life that took him into criminal psychology but does not elaborate.

Olivia and the parallel Fringe team allow John time to recover in the bathroom before tracking this new case, but soon discover he has escaped.

The two Johns briefly struggle with the idea of their doppelgangers, but soon learn that while they shared the same youth, their paths diverged when their respective fathers discovered their cache of dead animals.

He was later rescued by a woman named Marjorie (Enid-Raye Adams), who, even after seeing the dead animals, loved and embraced him, telling him "Even when it’s the darkest, you can step into the light", a phrase he has since used to subdue his homicidal urges.

Throughout the episode, Walter (John Noble) has covered up every reflective surface in his lab, trying to avoid the vision of Peter (Joshua Jackson) that he sees.

[2] "One Night in October" was watched by 3.1 million viewers, a 1.2 ratings share, approximately 20% less than the 4th-season premiere episode, "Neither Here Nor There" from the previous week.

Club writer Noel Murray graded "One Night in October" with an A−, explaining that it "was a terrific hour of television, making excellent use of the resources Fringe has available to them right now, both behind the camera and in front.

"[4] Entertainment Weekly contributor Jeff Jensen praised Anna Torv's dual performance and called the episode premise "clever."