Thawne stops short at the door of the time vault, and for a second the cautious euphoria that's come from having played Eobard Thawne at his own game turns to lead in Barry's gut. Cisco and Caitlin (and Barry) need them; Barry needs to get home to his own time before the wraith catches up to him, but Thawne clearly needs to have another last word.
"You are remarkable, Barry Allen."
Barry's fist clenches reflexively around the time drive, his hard earned prize. It's Wells' familiar whisper and Thawne's familiar praise, but he's had a whole day to prove he's not the same Barry as he was a year ago and now the juxtaposition sets off a cascade of warning bells under his skin.
As if he wasn't strung out enough already.
Barry rolls his shoulders in a kind of disinterested shrug to pretend that they haven't tensed up, like the Speed Force isn't screaming fight or flight through every nerve ending in his body. He'd like to say something cocky, something flip like, "I kinda get that a lot (so it doesn't mean anything, coming from you)," but the best he can do is pull a breezy grin and try not to shudder at the way Thawne picks him apart with his eyes.
"I always knew you would be capable of a great many things," Thawne continues in that same low, warm tone, "but your capacity to surprise me at every turn is one of your more rewarding - albeit frustrating - abilities." His words take a smiling, derisive turn at the last, but they're still shot through with the kind of quiet ardor that doesn't convince Barry to stop feeling like he ought to run.
"I find it remarkable that in so short a time you appear to have exceeded my wildest expectations. You, Barry Allen, are a remarkable human being." His sentence concludes with peculiar emphasis on each of the last two words, almost an insinuation that humanity may not be among the few traits they share.
Obvious time travel aside, the sentiment takes Barry back to that place where he had known Wells - Thawne - was an enemy, but couldn't yet shake the natural instinct to trust him. Buried deep in the neanderthal part of his brain there's a hardwired reaction to these words in this voice, entirely at odds with the way Barry can't look at him without the truth gnawing sick, angry holes in his heart . . . .
Barry's grin slips. He palms the back of his neck, at a momentary loss, conflicted. "Guess so."
Thawne's smile is tight, reproachful. "I know so." He shakes his head and puts his hand to his brow for a moment, rubbing at the creases of this borrowed face. "But do you know what surprises me the most, Mr. Allen? Can you guess - out of all of the wild, ill-conceived, idiotic things you've shown me today - the one thing that I never, ever expected from you?"
Just as familiar and unwanted: Wells' lectures. He seriously has better things to be doing than standing here doing this. Barry's shoulders square up, manipulated into the defensive. His hand slips from his neck to help phrase his speechless wonder with an empty shrug. "Please, tell me," he bites, sarcasm rising. "Teach me something, Eobard Thawne."
Something like electricity snaps through the air. It hits Barry hard, the reality of it all, that this isn't just a game he can reset or redo if something goes wrong. This time is still live, still fluid, and this is really Eobard Thawne, the Reverse-Flash - his mother's murderer - standing unmasked before him. (It's that moment that he starts to wonder if he'll ever be able to outrun this man's spectre.)
His nemesis offers him a benevolent smile that slowly creeps across his face, pulling it tight with some simmering emotion Barry's hesitant to name.
"The letter," he says. Clearly, with meaning.
Barry blinks. "The letter." A question.
Thawne's grin is toothy with wicked humor. "Your insurance, Mr. Allen. The secret letter stowed upon my sleeping Barry, the one that would foil me and my life's work - unless I let you, this you, live. That letter."
Barry blinks again, but slowly, feeling some of that bravado leach back into him. Out of all of the lies Barry spun in the heat of the moment, this is the one Thawne has decided to unravel. The drive in his hand feels warm, proof that he is allowed some sense of triumph for his efforts. His spine straightens and he crosses his arms, leveling a cool gaze at Thawne. "Took you this long to figure it out, huh?"
"There was no letter," Thawne says, needlessly.
"That surprises you?" Barry shrugs, mocking, "That I'm quick on my feet?"
Thawne laughs, Wells' brittle bark, and wags a finger Barry's way. "No, no, Barry. The bluff. The Barry I know - the Barry you were a year ago - he's many things but a liar he is not. Not a good one, anyway. Not as good as you."
Barry stands his ground as Thawne sways nearer, a predatory glint in his eye. "So who taught Barry Allen to lie like that?"
Barry swallows hard, lifts his chin. Gives Thawne the answer they both know is coming. "I had one hell of a mentor."