After he misses his mother too much the flash decides to run back in time and prevent her death, whilst he’s successful he completely changes the timeline with big consequences such as his loss of speed, a war between atlanteans and Amazonians had sparked out
Barry must regain his powers, assemble whatever the kind of justice league with faces he doesn’t recognise (yet) can and fix the timeline while having reverse flash trying to stop him so he has to live with his mistake
