The main story is Superman + Green Lantern, but more importantly, this contains a preview comic for The New Teen Titans.

Robin has been called in to stop some terrorists who have occupied a STAR building and are threatening to detonate a new device–a 'solar reactor', created by Dr. Silas Stone. When Robin rushes toward the building, he suddenly feels dizzy, then finds himself standing outside Titans' Tower, accompanied by Donna Troy.

The Teen Titans have apparently been called in–but Robin doesn't know anything about them. As far as he knows, the Titans disbanded months ago, and he has never met Cyborg or Starfire. There's little time to resolve the mystery: Raven appears and tells them that a scientist (Stone, again, as it turns out) has opened a gateway to another dimension, accidentally allowing a giant single-celled organism to pass through. That organism, in order to survive, is converting Earth's atmosphere to methane, so it must be sent back to its home dimension soon, before the Earth is rendered uninhabitable.

The Titans rush off to fight the giant alien blob, but their attacks prove ineffective. In the midst of all this, Robin briefly finds himself (not to pretend ignorance) back in the past, his present, where he must deal with the terrorists. He enters the building, but doesn't get far before he finds himself back in the future, fighting the blob.

The blob is a fearsome opponent, but they eventually send it back by evacuating the air from the lab, allowing Starfire (who doesn't need air) to force it back through the gate.

In the end, Robin finds himself back in the 'past', unsure what has just happened. We see Raven, who was the cause of Robin's premonition, watching him.