Plot Summary

Cobalt Blue, a one-shot villain that Barry Allen (as Flash) and Wally West (as Kid Flash) once faced has returned with a vengeance. With his mystical blue gem, he has targeted the Flash, and can use his gem to absorb the speedster’s speed. Flash is barely able to defeat Cobalt Blue, but is in for a shock when the villain unmasks himself: the person called Cobalt Blue looks exactly like Barry Allen.
 
Wally discovers that Cobalt Blue is Barry Allen’s twin brother, who was adopted by the Thawne family as Malcolm Thawne. Malcolm Thawne discovered his twin brother’s secret identity, and decided to destroy his “good” brother’s legacy. Thawne reveals that, just as the Flash legacy will live on for generations, so will the Cobalt Blue legacy. For every Flash that will exist, there will exist a Cobalt Blue set to destroy them. A mystic created a blue gem, and imbued it with power. She also told Thawne a prophecy:

A thousand years will the blue flame burn, granting your fondest wish… consuming not one Flash, but two… before at last claiming the life of your greatest enemy… Barry Allen.

 

Wally defeats Cobalt Blue, but is worried about the prophecy. With every speedster from the 20th to the 30th century in trouble, Wally decides to do something. With Malcolm Thawne in the custody of Central City PD scientist Angela Margolin, Wally recruits Jay Garrick, Jesse Quick, Max Mercury, and Impulse ( Bart Allen) to travel through the timeline and warn speedsters of the danger and the prophecy. Wally splinters off shards of the mystical blue gem, and passes them along to the speedsters. He plans on using the splinters as a homing signal to detect Cobalt Blue’s magic. Wally warns though, to not visit the early 30th century time where Barry Allen retired before his death. Using the Cosmic Treadmill, the speedsters went out through the timestream.
 
As the speedsters traveled through time, they used their slivers to key into times with other Flashes fought other Cobalt Blues. The speedsters from the 20th century warn other speedsters, who warn even more others. The speedsters also pass along slivers as well. At each timeline, the Flashes help their counterparts defeat that era’s Cobalt Blue. Some of the speedsters are familiar ( John Fox, XS of the Legion of Super-Heroes, Tornado Twins Don and Dawn Allen, Kingdom Come’s Kid Flash Iris West) while others are new to the legacy ( Jace Allen, Sela Allen, Thondor Allen). Wally also comes into conflict with the Reverse-Flash, whom he now knows to be the descendant of Malcolm Thawne. Also along the way, the Flash from the year 2231 is the first to die at the hands of a Cobalt Blue.
 

While the speedsters continue to spread the word, three of the teenage speedsters (Impulse, XS, and Kid Flash) decide to go to the 30th century and protect Barry Allen, against Wally’s wishes. When they get there, however, they start fighting each other. Wally follows them, and he too is filled with hatred. Realizing that the shards are causing it, he tries to rid the other speedsters of their shards, but too late. Cobalt Blue has possessed Jay Garrick, and now mentally controls all of the speedsters between the 20th and 30th century with two exceptions: Wally West, and Barry Allen. Barry comes to save Wally, and they two regroup and free Jay Garrick. The three Flashes free the other speedsters, but are unable to prevent the prophecy from being fulfilled: after all the speedsters but Barry and Wally leave, the living flame of Cobalt Blue kills Barry Allen.
 
With Barry dead, history has been changed. Without Barry there to stop his tachyon cannon, the Anti-Monitor has won the Crisis on Infinite Earths. After trying to stop the Anti-Monitor, Wally realizes he must right history. He travels back to the point right before Cobalt Blue kills Barry, and pulls Cobalt Blue away. Wally and Cobalt Blue are both destroyed, and Wally enters the Speed Force. Time has returned to normal, and a new Flash has arrived to replace Wally.