The degree and nature of Walter Bishop’s madness may not seem like the stuff of an exciting Fringe episode, but it sure worked out that way last night: This was one of the best Fringes yet for the way it wove its sci-fi with its emotional subplots with such tight, artful braiding.

The set-up: a number of mental-ward patients, institutionalized for 14 years each, are suddenly acting normal — good news, except that in the case of the first one, mental equilibrium was achieved by slicing off the back of his skull and removing… something.

The perpetrator of this theft was a familiar face, or head: Thomas Newton, himself a severed skull from the Other Side glimpsed by Olivia Dunham, and grafted onto a body in this universe. The hour’s central gimmick was ingenious: three patients, three bits of brain matter removed from them that wasn’t theirs in the first place — it had been implanted, which was what caused their mental distress. We soon learned these samples were meant to be re-implanted into Walter, that his own long-ago mental problems were caused (at least in part — don’t forget the hallucinogens he gobbled like candy in the ’60s) by these bits of missing tissue containing memories lost. Once restored in Walter’s head, this brain tissue might enable Newton and his First Wave army to extract information from him and build a doorway to the Other Side, which would have the rather unfortunate effect of destroying our world.

Science mingled with emotion this night, as Olivia assured Peter that, “Going crazy made [Walter] a better person, a better father.” And science mingled with action, as a gun-toting Olivia tracked down Newton, who’d injected Walter with a “neurotoxin” that would kill him in four minutes unless Olivia agreed to let Newton go free in return for the toxin-cure. This could have been a suspense-killer — no way was Olivia going let Walter die, right? — but instead, it set up even greater tension. “Now I know how weak you are,” the fleeing Thomas (“We’ve got what we need”) Newton cackled to the angrily compliant Olivia. He was right: She cares so much for Walter now that she’ll risk the show’s doomsday scenario (“opening a corridor” between universes that will result in “global destruction”) to save him.

Fringe at its best here is all about divided loyalties, the power of memory and the memory of power — how to get it, how best to use it, and how it corrupts.

This beautifully-directed episode (by Jeannot Szwarc, who’s worked on everything from The Rockford Files to Smallville) featured some gorgeously framed shots of bodies (Newton’s; Walter’s) entering the frame as gliding still figures.

A few final thoughts and a question:

• This was a great Walter episode. His emotional state has been played in the past for laughs (the eccentric with a child’s appetite for snacks), as evidence of mad-scientist genius (he makes connections and hathes theories quicker than anyone), and as tragedy (his commital to St. Claire’s hospital kept him apart from his son for years). This night, all these elements combined, along with some terrific scenes with Josh Jackson feeling guilt/anguish at all his father has been though, for maximum effect. Bravo, John Noble.

• Best exchange of the night: After Walter requests 50 milligrams of valium to calm himself, a doctor says, “That’s quite a high dosage.” “I have quite a high tolerance,” replies Walter.

• Best Walter non sequitur: “I have a terrible headache and a sudden craving for chicken wings.”

• What’s the significance, if any, of William Bell (brief cameo by Leonard Nimoy) using the name “Dr. Paris”?

Did you watch Fringe? I thought this was one of the best episodes yet; did you? And… no more Fringe until January! I crave more than chicken wings…