Work Text:
Eobard Thawne has a plan.
Eobard will assist Barry Allen in traveling back in time to save Barry's mother from Eobard's own destructive and malicious hands. While the Flash is occupied with his past-self, Eobard will use the time ship he's made to propel himself into the Speed Force.
Because he will be in the Speed Force at the time Barry changes the past, his own existence will be sheltered from the paradox Barry's stopping his past-self would create, allowing him to still exist as a product of his own actions, but erasing his actions from the timeline simultaneously. The Schrodinger's Cat of time travel.
The Barry Allen who returns to 2015 will retain his memories of the old timeline, in which Eobard killed his mother, but no one else will. The Flash would return to a world far different from his own, and to a group of people who may not even remember him.
They won't remember Eobard Thawne. His presence, as Harrison Wells, will be erased from their minds. The world will be as it was before Eobard meddled with it.
That also means that Cisco and Caitlin, and whoever or whatever may remain of S.T.A.R. Labs won't know he was there. The bomb he's building, far in advance of when it will need to be used, will not be detected in Barry's suit. Cisco won't know there's anything to check for.
All he will need is three seconds of distraction to insert explosives into Barry's spare suit, under the crest, at Cisco's work station.
The only thing standing in the way of his plan is the bomb's lack of completion. He'll be utterly free of the Flash, have his revenge. Eobard will snatch the happy ending from him one last time. It's going to be exquisite. It's going to be easy.
He runs a hand over his face.
So why can't he pick up the soldering iron?