Warning! The following contains spoilers for The Flash episode "The People V. Killer Frost." Read at your own risk!
The Flash Season 7 has had a trend of throwing a lot at its fans at once, and the series delivered a heavy one-two punch in its latest episode. Barry Allen may soon take on the greatest villain the series has seen yet after the Speed Force (which looks like Barry's dead mother) broke bad, and it came at a time when Killer Frost may very well be gone for good.
To tackle things in chronological order, the newly independent Killer Frost escaped the fate of having her powers legally erased by the state in her court case, and in the process, prevented a precedent that would protect future metas who ran into trouble with the law. Unfortunately, it took a drastic move on behalf of Frost, in which she recommended her prison sentence be elevated from 20 years in prison to life without parole. The move allowed Killer Frost to retain her identity with her powers, as well as protect future metas' rights in the court system.
The downside is that the harsh punishment potentially means that Killer Frost won't be on The Flash anytime soon. I mean, I absolutely expect The CW series to find ways for Frost to get out of the deal and join up on occasion, but considering she willingly wants to atone for her crimes and keep her powers, she'd likely return to prison soon after any team-ups. This could be the end of an era for Team Flash, who lost yet another meta ally at the worst possible time.
Barry and Iris weren't present at the trial and were instead with the Speed Force, following leads and hoping to figure out the identity of Fuerza. They were led to a woman named Sara Garcia, and in their conversations, realized that Sara was a good person with no idea what had been happening to her. Barry took Sara to S.T.A.R. Labs with the intention of rescuing her, but the Speed Force had other plans.
Before Barry could react, the Speed Force blasted Garcia with her energy and knocked her unconscious. Barry attempted to stop her with a blast of his own lightning, but the Speed Force merely mixed it with her existing power and seemingly killed Garcia with a second blast. As Barry and Iris looked on, horrified, the Speed Force informed the speedster it was time for him to choose a side.
Barry Allen is not in the business of killing, especially when he could be killing innocent individuals who have no idea what they're doing. He obviously doesn't subscribe to the Speed Force's "kill or be killed" mentality, but what can he do? Barry can't hope to destroy the Speed Force on his own, and even if he did, what would that mean for his own life? The Flash somehow found a way to make the speedster villain interesting again, and I can only imagine what help Barry will have to find in order to take her down.