Previously on Alias: Sloane double- and then triple-crossed Jack and Syd when the promise of a cure for his comatose daughter was dangled before his eyes; Gordo got captured and then sent on a mondo acid trip by Gonzo Geek Marshall, only to wind up murdered by Sloane in the end; and it was discovered that Prophet Five is actually made up of insiders at twelve government agencies. But you can forget all of that, really, because none of it makes an appearance in this episode.
We begin in Siberia on a train full of woolly Russian extras who look like they were shipped in from what's left of the Dr. Zhivago set. If you look carefully, you can see Omar Sharif in the corner, quietly playing bridge against himself. A man with a terrible haircut enters the car and trips next to two men playing chess. He then offers one of them the suggestion to try Knight to C-5 and the guy thanks him for this nice move. Terrible Haircut goes to leave and we see that he's left some sort of blinking device behind. He exits the car and sits down in the car right next to it and checks his watch. Seconds later, the device makes its final "ding" and we get an exterior shot of the train as a brilliant blue light explodes out of the car and immediately disappears. No one on the train seems to have noticed the explosion at all. Terrible Haircut goes back into the car with the bomb or whatever, and it would appear that everyone in the car has been completely torched, but their chairs and the interior of the car haven't been damaged one iota. Terrible Haircut grabs his device and leaves.
Apple Store. Marshall, Rachel, Getty and Dix are busy going through a huge stack of papers and documents. Rachel asks Marshall if he's decoded Gordo's encryption yet. Marshall says he would have, but he got a little sidetracked with some MI:6 transmissions he intercepted saying that there's been some talk about "M.P.B." tests. Getty and Dix are incredulous, but Rachel has no idea what the hell an "M.P.B." even is, so she asks Marshall what he's talking about. Marshall says it's a micropulse bomb, and it incinerates people but leaves everything else intact. By the way, a Google search for "micropulse bomb" just brings up eleventy descriptions of this particular episode, so I think we can count it out as being a potential real weapon, no?
Dix mentions the Siberian train incident, and Getty asks if that was the test, and no one seems to know, and Getty suddenly gets all breathless and declares that the Brits can't be going after an M.P.B. because that would violate every treaty known to man. Dix then says that Jack and Syd are in England trying to find out more about the entire situation and figure out who they can trust to talk to about all this. In the meantime, he says, they're going to spend countless hours going over every transmission Marshall pulled off the server. Mmmm. Exciting!