Participants:

Synopsis: Speeding through Central City, Barry Allen is met with a startling sight—the Flash, older, battered, and badly injured. Before he can speak, the doppelgänger is gone.
Then Barry begins experiencing glitches in his powers—moments that leave him ghostly and immobile in the middle of missions. When a group of his enemies—including Pied Piper, Weather Wizard, and Peekaboo—chooses this time to launch a new assault, the Flash seeks help from his most trusted ally.
Oliver Queen – the Arrow. [source]
Note: This post is for discussion of the book, so please be advised that there may be spoilers in the comments. As a reminder, LJ's spoiler code will work in comments and while it is not required to use when commenting, it is something that can be utilized to hide spoilers. (relevant LJ FAQ)