The Flash makes a rather significant guest appearance in Supergirl #16, which continues the “H’El on Earth” storyline that is being carried throughout the Superman line of books. For those who aren’t following this arc (you should), a mysterious Kryptonian named H’El has appeared with an amped-up power set that seems to eclipse even all our combined Supers. He has put a major wedge between Superman and Kara, rearranged Superboy’s DNA to the point that he has to wear Superman’s armor just to stay alive, and now plans to go back in time and “save” Krypton…at the cost of all life in our solar system! At this point in the story arc, H’El has taken over the Fortress of Solitude and attempted to block everyone other than Kara from entry. The Justice League has been helping Superman break in – including The Flash, who in the last issue of Superboy briefly appeared while trying to vibrate into the Fortress itself.
SOME MINOR SPOILERS AHEAD – PLEASE READ THE ISSUE BEFORE CONTINUING HERE!