Time travel is real. It’s experimental, unreliable, and lethal if not done exactly right. The human body isn’t even able to survive it, which is why STAR Labs created the Time Pool, a sensory deprivation tank that allows travelers to send their consciousness through time, appearing in the form of untouchable holograms.
It’s risky and dangerous, and why when Eobard Thawne, head of the terrorist group Doom, stole the most recent time travel device from Dr. Harrison Wells, the government decided to enlist the help of the most disposable people they could find-- prison inmates serving life sentences.
They choose three inmates--mob boss Leonard Snart, assassin Sara Lance, and Barry Allen, who was found guilty for the murder of his wife. With the promise of removing time off their sentences for time served, they send the three prisoners after Doom to save the timeline and stop whatever they’re planning.