Wow. Fringe's war between universes turned bloody last night. Both Walters decided to make some major sacrifices, and both Olivias faced some tough choices. Fringe is once again an epic drama. Spoilers ahead...

To be honest, I was starting to forget just how good Fringe can be when all the cylinders are firing on full. "6:02 AM EST" was fast-paced and full of insane twists – but also full of deep respect for the characters and their history. There were tons of little references to past episodes like "White Tulip" and "The Firefly," which helped cement our sense that the rapid decisions the characters were making had come from all the stuff they'd been through.

In "6:02 AM EST," Walternate and Walter both decide to sacrifice Peter for the good of their world – and it doesn't seem to work out that great for either of them. First Walternate figures out that he can extrapolate enough of his son's DNA from his grandson to activate the ancient universe-juicing machine. This causes "our" universe to start breaking down: sheep go nuts and then are vaporized, bats and locusts fly out of control, whole forests are wiped out. (It's interesting that sheep are among the first victims of the machine, since the other universe has no sheep.) Faced with an impossible situation, Walter reluctantly agrees to let Peter try and shut down the universe-juicing machine from our side.

Unfortunately, activating the machine seems to cause breakdowns in our universe, but doesn't appear to be improving the stability on the other side. (You have to wonder if Walternate "cheated" on the big choice Peter was supposed to make, so he doesn't get the expected benefits.) And when Peter steps up to the machine, it rejects him so violently, he's knocked on his ass. Peter's left in a coma, and both Walters are left groping for a way to save their world.

The episode does a great job of laying out the relationships between the Walters, the Olivias and the one and only Peter. In our world, we see Olivia and Peter finally sharing a bed, and looking quite cozy... except that it's Tuesday, the day Walter roams around the house naked, making revolting mushroom innuendos. Peter and Olivia seem to have worked through their trust issues, thanks to Peter recognizing Olivia's inner child last week. It's all so perfect, you know it's all going to go down the tubes soon enough.

Meanwhile, on the other side, Fauxlivia is fully bonded with her new baby, Henry, who's one of the most scarily calm babies on television. And Walternate still feels warmly towards the mother of his grandchild – even after she questions his decision to set off the universe-juicing machine. And Walternate has fully rejected the son he spent so many years searching for, saying "Peter chose to leave. He chose his allegiance." But Fauxlivia still has strong feelings for Peter – strong enough to make her go rogue and attempt to cross universes to bring him back so he can stop all this universe-juicing nonsense.

(How many people, watching this episode, thought Fauxlivia was going to succeed in crossing over, so she could find Peter just in time to talk him out of going inside the machine? There was a nice bit of misdirection there – it seemed like something would happen to delay Peter's big moment of self-sacrifice until the season finale, but then it went ahead and happened last night anyway.)

So Fauxlivia tries to steal a couple of universe-traversing wands, only to discover that they don't quite work. (And nice explanation, by the way, for why Walternate was so desperate to discover the secrets of cortexiphan when he already had a method of crossing between universes.) Fauxlivia's plan fails, and she winds up in what looks like the same cell the other Olivia was locked in last year. And Walternate tells her there's a parallel between them – he was willing to sacrifice his son to save the world, she was willing to leave her son behind to go get Peter.

Olivia, meanwhile, finally learns the truth about Sam Weiss' prediction that whichever Olivia won Peter's heart would also save her universe. (A prediction that we're all probably glad turned out not to be true.) Nina Sharp finally comes clean about Sam Weiss being the mysterious author of those "First People" books – but Sam has disappeared, because he was warned of the coming disasters by the click-clack 1970s office balls in his drawer. Olivia has to go searching for Sam, but then he turns up just as she's giving up hope. Sam tells Olivia to take him to the machine, and that she has to trust him. (Don't trust him, Olivia!) Oh, and Olivia doesn't even get a chance to deal with the fact that Peter chose to go into the machine without even telling her first.

But the real genius of the episode, not surprisingly, comes from John Noble, playing two anguished versions of Walter. Walternate quotes Oppenheimer and generally shows every sign of being racked with guilt for destroying an entire world, but he lives with his guilt with the same uptight, repressed attitude he greets every other emotion with. By contrast, Walter is operatic in his grief and despair at having to let Peter go to what he thinks is his death. After months of Walter agonizing over Peter's fate, we see it all come to a head, and acceptance does not come easy for Walter. The clip up top, where Walter talks to Broyles about it, is startlingly moving, as Walter tries for Walternate's stoicism and falls far short.

It all culminates in the chapel scene, where Walter has a long conversation with God, the entity whose existence he was denying so vigorously a couple years ago. Walter thought that God had forgiven him for his unforgivable crimes because of the white tulip he got in the mail – not realizing the white tulip was actually a result of Robocop's timey wimey. Walter finally accepts that he can't be forgiven, his sins are too great, but he begs God to spare his world – and honestly, let's hope that's as far as this show goes into spirituality. We still remember the weird Bible-toting FBI agent from season two, even if we can't actually remember her name.

Will Sam Weiss help Olivia bowl a universe-saving strike? What can Walter or Peter do to stop the cosmic melt-down now that the ultimate sacrifice has failed? I guess we'll find out in the next couple of weeks – it's going to be a long wait.

To tide you over, here's the first sneak peek from next week's episode: