Until last night's thrilling episode of Fringe, I don't think any television show had actually put me on the edge of my seat in quite some time. Sure, suspense is fun, but "What Lies Below" took suspense to a whole new emotional level.

Sticking with the shut-in theme established on Fringe's Thursday night lead-in, Bones, the Fringe Division investigated a curious viral outbreak that caused victims to spray blood from their mouths before dying. Not as gross as it sounds, but still pretty freaky. Interestingly enough, theFringe Division did not focus its efforts on where the virus came from or who its carrier was, but rather how the virus acted and how it could be cured. In other words, more "science" and less "fringe." Lucky for us, mad scientist Walter (John Noble) was in peak form, managing to scare kids, get arrested, and find a cure for the virus all within one episode. Well done, sir.

But the episode's real intensity came from Peter (Joshua Jackson) and Olivia (Anna Torv). Both of their stubborn sides really emerged in this life-or-death situation—Peter refused to tell anyone he was infected until it was too late, and Olivia refused to let him out of the quarantined building. The tension mounted, the anger grew, and Peter finally confronted Olivia violently, claiming she had betrayed him. It's a scary thing to see two characters—who have grown so close over the course of a season—defend themselves against each other. And though the two made up at the end (Olivia blamed Peter's outburst on the virus), their duel will inevitably affect their relationship.

Another relationship that changed in this episode was the adorable father-daughter-esque one between Walter and Astrid (Jasika Nicole). In his haste to find a cure to heal Peter and the rest of the infected people, Walter let it slip that he couldn't "let Peter die again." And when Astrid called him out on this little utterance, Walter responded with a somber, "Some things are meant to be left alone." Ouch.

What's next onFringe? Who knows, really, but isn't that why we love it so much? I hope Astrid gets sucked into the alternate universe. Sooner or later she'll have a few questions for William Bell (Leonard Nimoy), and he's due for an appearance, anyway.