A review of tonight's Person of Interest coming up just as soon as I perform brain surgery on a moving subway car...

"6,741" is very clever in how it sets up its devastating final twist. Everything about Shaw's escape from Samaritan captivity feels off, which should point us to the idea that — like the Machine's simulations back in "If-Then-Else" (Shaw's last episode as a regular member of Team Machine) — this is all going on inside her head. But the episode elegantly sets up an equally plausible, more overt theory: that Greer let her go because she's been reprogrammed by the chip in her head more than she realizes, and will go full Manchurian Candidate on Root, Reese, and Finch at the worst possible moment. This is all part of Samaritan's larger game to get Shaw to reveal all she knows about her comrades, but it seems so obviously what's happening — at least until Shaw puts a bullet in Greer's head, in a manner seemingly far too quick for the human face of the show's chief villain, then shoots Reese in the heart — that the revelation of what's actually happening hits even harder.

"It was all a dream!" can be one of the laziest storytelling devices, but it can also be incredibly powerful in the right context. Here, we want Shaw back on the team because she's awesome, and we want her and Root to finally hook up (to the strains of Nina Simone, no less) because of course we do, and we want her to be able to escape Samaritan's control because we like her too much to have her consigned to that fate. And in the end, we discover the fate is even worse than we realized: that the episode's title details how many times she's been forced to relive some variation on this, from the cruel tease of finally getting to spend a night with Root to it all falling apart, again and again and again.

A great episode, and a great spotlight on Sarah Shahi, who made her entrance into the series with an episode where she also took over the show like this. Now that CBS has passed on her adult Nancy Drew series, she's available again, and "6,741" provides yet another excellent calling card for why someone should be racing to hire her to front their next series.

This is the last of the four episodes CBS sent out in advance (and, thus, maybe the last episode I'm going to review for a bit), and the strongest one of the bunch. It was cruel, but in a way the show needs to be at this stage of things.

What did everybody else think?

Alan Sepinwall has been reviewing television since the mid-'90s, first for Tony Soprano's hometown paper, The Star-Ledger, and now for HitFix. His new book, "TV (The Book)" about the 100 greatest shows of all time, is available now. He can be reached at sepinwall@hitfix.com