This review may contain spoilers.

Let us take a moment to appreciate the last new "Fringe" episode of 2009.

Alright, moment over.

This episode started off strangely enough, opening in a place called Hennington Mental Health Institute. We see Thomas Jerome Newton (Sebastian Roche) -- first (and last) seen as a head being attached to a corpse in "Momentum Deferred" -- performing some sort of procedure on the back of a mental patient's head. The patient, Mr. Slater, is wide awake and waxing insanity about a girl in a red dress. However, this all stops once Newton removes something from Mr. Slater's head. Newton and his crew rush out of the institute, without even stitching Mr. Slater's head back up, and with "Fringe" leaving us all a pretty gruesome image of a person's exposed brain.

As one would assume, this gets the Fringe Division's attention, but mainly because after whatever Newton, Mr. Slater was "cured" of his insanity. And Mr. Slater wasn't the only person this had happened too -- other people who were normal one day and crazy the next were cured, with no memory of the unauthorized surgery.

The common denominators are a man named Dr. Paris (who referred these "insane" people to the institute in the first place), a scar on the back of their head, and appearing and disappearing brain tissue. Apparently, if a person is implanted with just a bit of someone else's brain tissue, they lose their mind. The Fringe Division -- well, mostly Peter (Joshua Jackson) -- immediately assume that this Dr. Paris character performed the same brain tissue transplant on Walter (John Noble), and are seemingly proven correct by him having the same scar on the back of his head. An even older scar. Despite Walter claiming not to have ever had any visitors in the 17 years he spent at Saint Claire's, records state that Dr. Paris came to visit him on six different occasions.

Even more shocking to the Fringe Division was the fact that Walter wasn't implanted with someone else's brain tissue -- his brain tissue was removed and was the same tissue that turned these other people insane. These parts of Walter's brain hold the "secret" of how to pass between this world and the other side -- something that Newton greatly wants to know. Proving that he is a real evil genius, Newton not only gets the information that he wants, but he escapes to twirl his metaphorical mustache another day.

Oh, and Dr. Paris? It turned out that was just an alias for William Bell (Leonard Nimoy). He actually removed Walter's brain tissues for non-evil reasons -- he realized just how dangerous it was for his friend to have this information and wanted to protect him. The plan didn't really work, but it's the thought that counts, right?

What Worked

From the moment Olivia (Anna Torv), Peter and Walter drove up to Hennington Mental Health Institute, it was obvious this was going to be an interesting episode for Walter. While most of the episode was very emotionally heavy for Walter, there was definite amusement in Walter's brief interaction with a security guard (when he reply to the security guard's simple question if he is Walter Bishop by answering, "Yes. I'm perfectly sane.") as well as him awkwardly greeting people in the mental institute (in the background, while Peter and Olivia endure exposition). But as usual, once things got serious, John Noble was able to perfectly portray that broken Walter, the one who lost his son and his mind.

As a pre-hiatus episode, "Grey Matters" certainly worked. It provided enough intrigue to keep fans excited for the show's return in January and just continued this season's streak of great episodes.

What Didn't Work

This is really a small nitpick, but anyone who saw Leonard Nimoy's name in the credits for this episode probably could have connected William Bell to the mysterious "Dr. Paris."

Giving Credit Where Credit Is Due
"Fringe" stars Anna Torv, Joshua Jackson, John Noble, Lance Reddick, Blair Brown, Jasika Nicole. "Grey Matters" was written by Ashley Edward Miller & Zack Stentz and directed by Jeannot Szwarc.
"Fringe" airs Thursdays at 9 p.m. on Fox.