The episode follows Peter (Joshua Jackson) as he continues to stay away from Boston after learning his true parallel universe origins; his travels take him to a small town, where he helps the local police investigate mysterious disappearances.

After learning his true origins in "The Man from the Other Side", Peter (Joshua Jackson) leaves Boston and travels to a small town in the state of Washington.

Peter decides to aid them in the investigation after catching a glimpse of Thomas Jerome Newton (Sebastian Roché), believing the shapeshifters are responsible and are coming after him; however, he does not wish Walter to be involved, asking Agent Broyles (Lance Reddick) to keep his location secret.

During the autopsy, Peter explains to Sheriff Mathis (Martha Plimpton) how removing a part of a brain could provide information to the killers.

Peter begins to doubt the shapeshifters' motives after another body is found, but eventually comes up with an idea to read and track the victims' adrenaline spikes, which allows him to find where the murders took place: a dairy farm.

"[3] Miller continued that at the time, he and Stentz thought they were writing Olivia-focused episodes, but "In retrospect, we really wrote a four-part story about Walter, his relationship to children, and the struggle between Walter-who-was and Walter-who-is.

"[3] A fan of Fringe, Pearl Jam musician Mike McCready talked with series composer Chris Tilton about writing some music for "Northwest Passage".

[2] Twin Peaks was originally titled "Northwest Passage" before its pilot, and both focused on solving a murder mystery in Washington state.

The Sheriff played by Martha Plimpton has a pen with "find the crack" printed on it, she states to Peter Bishop "that's how the light gets in."

SFScope writer Sarah Stegall speculated that the episode's "standalone mystery", combined with the recent Fringe season renewal, helped contribute to the ratings gain.

At times tonight the show almost felt like a backdoor pilot for a new series, with Peter tooling around the Pacific Northwest meeting local law enforcement and cracking cases.

And while that's a show I'd definitely watch, I confess I'm anxious to jump ahead to next week, when there'll be inter-dimensional conflict and doppelgangers galore".

If the plot had holes you could drive a starship through, the episode was still redeemed by top notch acting, the X-Files ambiance, and the new dimensions added to our knowledge of Peter.

[13] Stegall concluded her review by praising all of the actors' performances, explaining that other than the "clumsy" killer plot twist, "I had no complaints at all about this episode.

[13] Ken Tucker from Entertainment Weekly enjoyed how the episode mystery was processed from Peter's point of view, and loved the revelation at the end about Walternate.

[1] After trying various science fiction shows after Lost, the Los Angeles Times' Andrew Hanson felt the episode made "him feel like [he] picked a winner".

"[15] At the time, TV Fanatic called "Northwest Passage" the best Fringe episode to date, giving the series' its first "five out of five stars".